You can sort of do this, and Sow Thoughts is hardly fleeting. Quite the opposite actually.
Sow Thought's greatest asset is its permanent duration. Even if your target recognises later that the thought is not their own for some reason (e.g. because it wont go away no matter what they do) they still have the thought. You can (and I have in games before) use Sow Thought to make a person do what you want, you just have to be clever about it (just like with the suggestion spell) and it's not going to work, for example, in the middle of combat. Times my Changeling Witch/Mage of the Veil used this to control people:
The senate of a newly founded nation held their first meeting. I was the chef. Using my Cauldron hex I brewed up a course of Sow Thoughts Truffles, Portabella Polypurpose Panacea Patties (with pickles, provolone cheese, and poppy seed bun), and Guidance Gumbo. I fried the patties in oils of Mask Dweomer to conceal the magic of the food, and coated the truffles similarly. When the senate began talks, they were heading towards a militaristic oligarchy. When they ended thoughts they were a (very) idealistic egalitarian republic that had also decided to appoint me Grand Advisor of the Nation for some reason. Because the senators were discussing political theory and the nation's plans and the potions inserted concepts like "Liberty, Fraternity, Equality" and "Vox Populi Vox Dei" into the discussion on multiple sides at key moments, the result of the meeting (and thus the course of the nation) could be determined.
Later, and in another land, a sexist human bigot decided to contest my growing authority as Patroness and Protector of the Material Plane, Beloved Goddess, Mother to All. A couple castings of Sow Thoughts left him with 1) the idea that he was currently hearing eldritch whispers crying "Flesh. Pain. Blood. We will tear you open. Our children will feast upon your bowels." in the Aklo tongue over and over again in an endless loop. 2) The concept of being in excruciating pain. 3) The suspicion that he had gone mad. Sow Thoughts is not beyond being overridden temporarily by the subject's personality, native thoughts, and will, of course, and so the nobleman scoffed at my curse, spat on me, and refused to accommodate the demands I was making of him (no more prima nocta, certain legal protections for children, slaves, and animals, 20% reduction in excise taxes on gambling for the lower nobility, tax exemption for my personally owned extra-planar magic item emporium). He went mad within 3 weeks and I put him down in the street when he (Sow Thoughts #4) begged for death. People didn't bug me about being female after that.
A particular paladin caught my eye as a potentially cool person. So I set myself up as a fiendish seductress, tempting him towards evil. I kept him isolated from his fellow knights for 6 months while he quested against me, during which time I poisoned his mind with more and more evil ideas, concepts, and suspicions seemingly designed to destroy his faith. He persevered and when he finally tracked me down and killed me (actually an illusion) I cast dispel magic on him and suddenly the mountains and mountains of doubt and hatred and evil lies that he had been tirelessly struggling against disappeared, while the coping mechanisms he'd developed remained, basically making him good-on-steroids for a while.
So, basically, you can't make someone your slave with Sow Thoughts by giving them the idea that they are your slave. You can do it by giving the idea that they are in a great deal of pain and the only way to make it stop is to serve you, or by giving you meaningless honorary titles (that turn out not to be so meaningless after all) because you were oh-so-helpful, or by using reverse psychology and then dispelling the curse.
You should note that Sow Thoughts is really much better at sowing beliefs (concepts you think are true) discretely than ideas, even though people do not automatically believe the concepts you sow. Because it lasts until dispelled, anything that isn't the sort of thing a person would normally hold unwaveringly for their entire lives will probably be noticed eventually, whereas concepts the person keeps coming back to are likely to be accepted eventually.
You should also only instil suspicions in people you want to cause to suffer, as permanent unshakable nagging suspicions are basically classic psychological horror material and usually drive their possessor insane.