Router jig for vertical milling

Does anyone have any good ideas for a jig?   I need to mill down logs of a log home that have rotted away due to snow buildup. I am thinking of a jig to run a router over the log to flaten out the damaged areas and then secure new wood cut from outside of new logs.  I would need to trap the router so it could move up and down as well as left to right while keeping a close tolarence.  Any ideas, or have you seen any articles?

Thanks, Larry