Thanks for all the suggestions. It really helps to have all the options laid out.

I will go with Devils_Advocate's suggestion:

The “Rule of Cool” must always be subordinate to the “Rule of Don’t Be Ridiculous.”
a. Support player ideas that are cool, creative, imaginative, and reasonable. That does not mean supporting ideas that are cool, creative, imaginative, and unreasonable.
b. If the idea is one you can see Aragorn, Conan, Captain America, or James Bond trying, then allow it – for the right character. [Don’t let the Conan-clone play the James Bond stunt.]


[I won't call it the Balki corollary, because I never saw Perfect Strangers, and never knew who Balki was until I followed your link. I started playing D&D in 1975, more than a decade before Perfect Strangers. But you are free to call it anything you like.]