How to add BL51 directive in Library?

I have created a small timer library, in which it call the timer handler by function pointer in the interrupt.And i now found that the handler local data would be corrupted because of the data overlaying.But i created this library to let others use it, but they would be bothered about data overlaying. so is there any way to exclude a function from overlay analysis when the user add the function as a timer handler by calling my library,or at least ,disable data overlaying when anyone use my library?
OVERLAY directive is a linker directive so it seems no way to use it in the source code.....