Well, this seems to work so far but I'm too new to scripts to give it a proper test. Here's what I did:
1. Download the 64 bit MSI installer
here
2. Used
these instructions to install Python on my USB stick. I did a full install into a subdirectory.
At this point there's a little niggle. Even though you tell the installer to use the USB stick, it puts the python32.dll in c:\windows\system32. I simply moved it into the top level of the subdirectory I created in step 2. I went into preferences and enabled scripts, browsed to the subdirectory on the USB stick and Reaper found the .dll. To test, I created a Test.py file with 'RPR_APITest()' as the only line. Seems to execute fine, I get the 'test OK' message.
At this point I'm about as far as I can go testing wise. Maybe over the next couple days I'll get a chance to play with it a little more.
Edit: I don't have any reason to try it but I imagine this would work with the 32 bit MSI as well. That's assuming this actually works and I'm not barking up the wrong tree.
Edit 2: Got to thinking that browsing for the path is a bad idea. It will include the drive letter which may not be the same on a different computer. Entering \<subdirectory> in the 'Custom path to dll directory' field seems to work.
Edit 3: Oy. This works but it's not portable. The search continues.