[Exim] Looking for a driver/router/transport that will do qm…

I have a domain with a lot of qmail-style aliases that I am
loath to lose, but I want to put it on an exim machine.

Rewriting the .qmail files in, say, procmail format is not a
problem.

Neatest would be to have a router or a transport in exim that
would simply choose the appropriate (procmail or qmail-native)
delivery file. Does that exist already?

If not, I'm off to put a qmail behind the exim, on the same
machine; that should work, but the poor 486 32Mo in question
doesn't need the load.