Single .ISM, multiple release targets; different INSTALLDIR targets, what's best way?

Hi have a single single .ISM Basic MSI project.

Under releases I have 2 different targets: 64bit, and 64bit-BETA. Each release needs to target a differently named installation directory.

For example:

c:\program files\MYPRODUCT
and
c:\program files\MYPRODUCT-BETA

What's the easiest way to accomplish this?

I probably have glossed over the right way to do it and got mired in the wrong way ... but what I had done was to add different release flags to each of the releases: then during the install, if BETA -- add "-BETA" to the installation directory. But I'm sure you will spot the problem right away.

Changing INSTALLDIR after CostFinalize doesn't update all properties derived from INSTALLDIR (not quite sure how the UI Dialog figures out how to do it when manually changing the install directory!).

Before CostFinalize, I don't know what the base (or original) installation directory is. If I could extract before CostFinalize, I'm OK with that.

Thanks,

Wim