This is a simple trick that I use at work (my project suffers from a similar problem, tons of small requests, far outstripping our capacity to fix them): ask the requester to file a bug, verify and acknowledge the problem, and then usually ignore it for a loooong time. It is actually a somewhat useful thing to have all the bugs in one place even if nobody is working on them, sometimes you can look at all the bugs together and find a common problem.