Portable holes are your friends.
Quick and dirty answer: a scroll of stone to flesh (lvl 6 wizard), a scroll of flesh to stone (same), and a portable hole (20,000 gp). There are a few issues with this one. There's a fortitude save 15 at the end, and if the target fails that one, they die. Given that having them dead is apparently not an acceptable alternative (and, by extension, that they'd resist attempts to raise dead) they might just choose to fail that save. Also, you need someone to successfully cast 6th-level wizard spells from scrolls, and you may need to do it more than once if you can't get them to fail their initial saves voluntarily.
No consumables answer: a portable hole (20,000 gp), a ring of sustenance (2500 gp), and a necklace of adaptation (9000 gp). This assumes that he's not willing to suffocate or die of dehydration, that he's either not willing or not able to deliberately kill himself, and that he's not able to escape an extradimensional space by himself, once otherwise stripped of gear. If the target is capable of dimensional travel, but not capable of generating a +10 strmod, then Dimensional Shackles (28000 gp) will handle that issue.
Or you could lob him through a Gate
Gate is a 9th-level Cleric/Wizard/etc spell, and will let you open up a gate to throw him through (into the prison cell). It's not entirely impossible that you might be able to field someone who could cast that off a scroll. It might get pretty expensive, though, if you start having to deal with a failure chance. Each scroll will run you 3825 gp.