I could have sworn there was some way to get more use out of a weapon oil somehow. Of particular interest to me right now is the Bladeshimmer oil (Complete Scoundrel pg114). As it is, it only works for the first attack, is there any way to make this last more than one attack or even perhaps indefinitely?
Bladeshimmer is a Wondrous Item, not a magic oil, and is subject to different rules.
Going by the rules on oils in the d20srd, oils are spells in liquid form that you can apply to stuff. This means that when applied to a valid target you get the effect of for example Shillelagh for a duration that matches the spell description.
Bladeshimmer, while being described as an oil with a magic effect, is not a magic oil. It is a Wondrous Item, stuff you can put on an object to make it invisible for an indefinite amount of time, or use it to get a one-time bonus. If you read closely you see that Bladeshimmer has no duration, meaning it will remain in effect until wiped off or is used to get a flat-footed bonus with an attack. So while Bladeshimmer is a magical oil it is not a magic oil as in the external equivalent of a magic potion, and it uses different rules.
So no, this effect cannot be made to last longer than 1 use because it is how the Wondrous Item was designed.