What if I need more than SIGUSR1 and SIGUSR2?

POSIX defines only 2 user-defined signals. What if I need more than that?
I guess one way is use one of the less used signal, for example:
#define SIGUSR3 SIGWINCH
But which are the less frequently used signals?
I read that there are some user-definable, real time signals: SIGRTMIN+n through SIGRTMAX. ("On Linux 2.6, LinuxThreads uses the first three real-time signals, so threaded applications that support LinuxThreads should not use these signals for their own purposes." - from Wiki) Can I use those, even if I am not writing anything real-time?

Why whould you need so many?

I inherited a middleware that already used SIGUSR1 for signalling a 'thread injection' and SIGUSR2 for some fault tolerance/checkpointing purposes.