[exim] How to - forward, then freeze original

I would like to be able to detect certain things within a message (this
part I can do) and if found, forward the message to a new recipient and
then freeze the original message.

I'm thinking something like a dnslookup router with unseen=true, followed
by a redirect router with data=:freeze: (all with the proper conditions of
course).

Does that make any sense? Has anyone out there done something similar?

Thanks,

Dan