That depends on what he's trying to do, Anil. If he just needs the PHP code, then yes, he could just capture that code and eval() it. Even if the output of the code is conditional, if he knows what arguments the SSI call would normally accept, then he can still do it by having the Perl script supply those arguments based on input from server b.
In short, Eric, yes, it is possible. Implementing it would be tricky, but if you are willing to describe what you want to do in detail, I'm sure you'll get plenty of help from this forum.