The Jopr plugin container (PC) only supports hosting RHQ/Jopr plugins. There are a couple ways you could go:
1) Write a postfix Jopr plugin.
2) Add support to the PC for hosting Hyperic plugins.
Option 2 would be significantly more work than option 1 and would also require an understanding of the innards of the PC, but it would have the advantage of allowing you to use other Hyperic plugins within Jopr.