In the Redemption FAQ there's a proposed solution to handle mismatched bitness by using:
app.CreateObject("Redemption.RDOSession")
The RedemptionLoader allows skipping COM registration by calling:
RedemptionLoader.new_RDOSession()
Is there a way to combine both of these features to handle mismatched bitness without registering the COM dlls?
I don't think you can using OOM, but you can create your own out-of-proc (exe) COM server that uses RedemptionLoader to create and return an instance of RDOSession to your process across the process boundaries.
Keep in mind that you can dynamically register redemption.dll in registry using regsvr32.exe even without elevated rights - it can register itself in HKCU instead of HKCR in case of limited user rights. Outlook won't have any problems seeing that COM registration.