Sharkbite makes "slip couplings":
Home Depot source
These are designed to slip deep over one end of a pipe, to allow a fix pipe like your PEX segment to get in place, then slip back for the final connection. The "About this product" section on the Hope Depot link claims that this device can handle a 2" missing segment of pipe. If you cut clean that damaged copper pipe end and properly size the length of replacement PEX, you can slide a slip coupling on the copper pipe and slip it back over the PEX end, and the repair is complete.
(The product is shown for example purposes only, I'm not affiliated with this product or Home Depot.)
Answer from Triplefault on Stack ExchangeVideos
These things seem like the perfect product. Does anyone have any long term experience with these leaking? How are they to work with?
Link: http://www.sharkbite.com
Edit:
Sounds like nothing but great things to say about them. I'll be using them as required. This latest project was a dishwasher installation.
Sharkbite makes "slip couplings":
Home Depot source
These are designed to slip deep over one end of a pipe, to allow a fix pipe like your PEX segment to get in place, then slip back for the final connection. The "About this product" section on the Hope Depot link claims that this device can handle a 2" missing segment of pipe. If you cut clean that damaged copper pipe end and properly size the length of replacement PEX, you can slide a slip coupling on the copper pipe and slip it back over the PEX end, and the repair is complete.
(The product is shown for example purposes only, I'm not affiliated with this product or Home Depot.)
Replace more (throughly unbendable) copper with (slightly bendable) PEX. If you can replace the copper to a point where it turns 90 anyway, one 90 and one straight will get the job done easily while (as @keshlam has already noted) the stock solution to a short splice in a stiff line is four 90's. In a longer straight line situation you can loop or wiggle the PEX (respecting minimum bend radius) or you could use 2 90's and a U-Bend (respecting minimum bend radius) of PEX between them. That might be better done to the next joist bay or the one after that to keep the bends large.
Do you need to remove the plastic piece inside of a sharkbite fitting before inserting copper pipe?
We are doing a total remodel on a house we just purchased. Noticed most of the angle stops are crusty or leaking under the sinks so decided to replace them all. They had compression fittings on half inch copper. After removing the fittings with a puller, I noticed that the copper is slightly crimped. Not a lot but it's visible. I'm planning on replacing the angle stops with SharkBite valves. Is it okay to install on that copper in that condition after it's been cleaned? I did install some temporary end caps that are holding well.