I am in no way a pro at this but I've had the engine broken down 3 or 4 times.

You'll have to pull the clutch and counter balancer weight & nut to remove the Cb shaft to replace the seal.

Plus you'd have to remove the seals without scratching the mating surfaces and you'd have to press the seals in correctly. 

IMHO since you're already going to be almost pulled apart I'd just split the cases and replace them correctly Vs. half a$$ing it and risking not having it done correctly and needing to do this again "in the middle of the season".

If you do this I'd get the case splitter from Tusk on RMATV, it's around $50, you usually don't need the crank puller if you stick it int he freezer. 

I'd also check to see if there is any play in the main bearings before you pull it apart so you know if you need to replace the mains while it's split or not.

that's