Those FM's work, but they are not Remote-Enabled Modules, so I can't call them from an external application. I'm connecting to SAP using the NW RFC SDK.
I ended up making it work by calling BAPI_FUNCLOC_GETLIST and setting the LOW and HIGH filter values to the same Functional Location string. It returns 1 result which has the matching TPLNR. It's not an ideal solution, bit it works.
Thanks for your help!