Does anyone have any idea how to do this?

The reason I ask here is because I'm using the port, not the stock
package from Mailman. I don't know if there's a generic way to change
the install location for any of the ports, or if each one would have to
be configured separately.

I don't know if the port differs from the original package at Mailman.
If it doesn't, I could just use compile that one. Anyone know?