can I change the source in whole directory to custom build (batchly)?

[huzhongshan]

In my project , I have a directory in which all files should be compiled by nasm. I add the whole directory to c::B, but I find that I have to change them to custom build ( nasm -fwin32 $file -o $object) one by one, the build command is exactly the same.

Is there a more easy way to do that , like just set the command in directory(suggestion) ?