The problem with this is that the upgradable tickets these days are way more expensive than they used to be. If you value points at a penny per and are looking at a TATL trip it is likely that the cheapest you'll get away with on the spend side is 50K points and several hundred dollars of co-pay fees, PLUS the original ticket price. Compare that with just paying the 100K points and having the seat in C issued and you're probably coming away with a lower total cost that way. There are certainly some exceptions, but for most of the US-based programs it is almost certainly a better deal to just redeem straight into C rather than ticket + co-pay + miles.