I just looked at the code for Scalar::Util and the non-XS version of refaddr does a stringify, then a regex match to pull out the hex number. Simply putting an arbitrary unique ID into my records and dereferencing it isn't all that expensive, so I think that's going to have to be my answer.

Since I'm doing pack, unpack hacks for the Guttman-Rosler-Schwartz transform, I was hoping for some pack/unpack wizardry. But if Graham Barr didn't use that kind of wizardry in Scalar::Util, that's very good evidence there is no such thing.

thanks, jeffrey kegler