The ActiveState Mac installer does not give any location options to install other than /usr/local/ActivePerl...

Are you sure ? I find that simply too appallingly limiting to believe.
But I don't use Macs.

It might be worth asking about this on ActiveState's Installation Support forum.
That would seem the obvious place to check ... but it's not very active, and it looks like you need to have (or create) an account to post there.
It might therefore not be worth the effort ...

Cheers,
Rob