I think that with the use of the rule indirection feature which allows rules to be invoked through variable expansions,

$(rule-name) x y : z ;

you can wrap up all the logic in one place and avoid the maintenance problems. I did a similar thing for response-file support in Boost.Build.

The code to implement the feature in Boost.Jam is pretty straightforward. Let me know if you want to see it.

-Dave