If you build the interpreter on Windows and create the installation package you should use a special build of NSIS that has support for long strings.
I've put together a zip file that has the special build of NSIS and put it on SourceForge at:
The file is: Nsis_shortStrings.zip
Just unzip the file and put the resulting directory in the place. The zip file already includes the plugins that need to be added to a regular install of NSIS, so it is easier to use the zip file than to do a regular install of NSIS and add in the extra stuff.
The ooRexx installer itself now detects if it was built using the too short string max version of NSIS and warns the user if it detects that.