Thanks hippo - that WriteMakefile() argument does exactly what I want.
And "macro" is a valid argument going all the way back to EU-MM-6.17 (and probably beyond) - so it should certainly suffice for a module that (intentionally) doesn't work on perls older than 5.22.0.
Cheers, Rob
Comment on Re^4: How to tell EU::MM to install a pure-perl module into an architecture-specific location