I've used both a page in the content tree and a page within the CMSGlobalFiles directory (which is in the Excluded URL list). The physical page in the CMSGlobalFiles directory works but isn't ideal because I'd have to write some code to do a check to see if I can access the database or a page.
When I use a page in the content tree I get a result something like this:
2013-07-01 00:00:00 10.10.14.31 GET /CMSPages/PortalTemplate.aspx aliaspath=%2fHome 443 - 10.10.14.140 HTTP/0.9 - - - 200 0 0 156
So it looks like I answered my own question here. I tested and used
/CMSPages/PortalTemplate.aspx?aliaspath=/Home
for my URL vs. the rewritten one and all works as expected.