If you're interested in the gory details, check out the proc(4) man page ("man -s4 proc"), specifically the psinfo and as files. psinfo contains two things to help you:

1. The first 80 characters of the original command line, basically, the string that /usr/bin/ps prints.
2. The address of the process's original argument list, within its address space. By opening the as file and seeking to this address, you can read the arg list out of the process's address space.

In principle, you could use perl to do either of these things. Hopefully you're familiar with pack and unpack.