[alasdair_]

For non-controlled substances, I've been able to ask for more from my doctor and just pay out of pocket.

For controlled substances, you could probably ask for a slight change in prescription (e.g. a single 20mg pill vs. 2x10mg) right after the first one was filled, or ask for a slight change in dosage.

Technically this is legally dubious, but it's also ridiculous that there is no buffer allowed to be built in.