You could configure different install and search paths for single- and double-precision versions of Pd. I don't know if they share the config file. If they do, you would have to adjust the config whenever you switch between them.
they do share the same config file on macOS at least. i solved this for me with this change here yesterday (it works - although I'm not sure if these changes are all correct and useful): https://github.com/ben-wes/pure-data/commit/18793a0192d41875af968cc6bd74ba58...
cheers, ben