Call Recording

I know I can use MixMonitor to record calls. It works perfect and Asterisk 1.4 save the file as gsm file which save a lot space.

Now I am trying something different. I want the call be recorded only when needed. So I try to use dial *1 to start the recording. This works but it creates two files in every call and both of them are big wav file. Is there a way to make this only record one mixed gsm file, just like the MixMonitor?