Mike's solution sounds like the best way to go about it. The problem with equating the number of pattern instances (pXX) to the real number value is that it always seems to round down.
This could be done with a user program as well. Pro/E's relations editor has a "User Prog" option that lets you link your file to a C program. I've never really been able to make it sing. Anyone had any experience with this? I have a part I made a while back with an attempted link to a simple C program, but I don't think I set Pro/E up for this correctly (there is an include file called "spgusrgl.h" and a few environment variables that had to be set up, and I don't think I did it correctly). Searching through Pro/E's help documentation for "User Prog" tells you about it, but it didn't really help me set it up.
Anyways, if you could make this work, you could write a simple C program to round these values for you.