Need help

Hi, I am developing a billing package for ISPs. I am trying to use the freeradius server, but my problem is that my database schemas are complex and won't be working with the available modules. That means I will have to develop a custom module for my software and compile it with freeradius. My problem is that if I do that, it won't be compatible with general RADIUS servers and I'll have to provide the software with freeradius server and my module. So will it mean that I'll have to keep my software GPL, since I am using and distributing freeradius and also it contains mysql server, or can I distribute my software commercially? Kindly help me and tell me what can be done regarding the same? Thanks in advance. Abhinay