As a first cut, I would scan through to find the tempsets, take out the variables, and then expand to a let or with block now that you know their names.
Ah. Right. (And I even worried about similar things when writing make-br-fn...). Well, it would work in simple cases, but let/with are looking like better ideas.
Actually, if we add another primitive (with $ or xdef) which works using mzscheme's namespace-undefine-value!, we could have tempset maintain a global list of tempset variables, and cleartemps go through and undefine them.
