[rurban]

Ouch, you are right. So the only strategy would be to switch to lexical compilation blockwise, while fixing the remaining dynamic extent vars.

[pzone]

Which is more or less the strategy in the Emacs codebase - the intention is to incrementally port to lexical binding on a per-file basis. (This is seen through the annotation -- lexical-binding:t -- at the top of many .el files.)