You'll need a couple of bags and some tie wraps or tape. Can also pull the wheels and only strap the frame to the carrier.

Have someone hold 1st bag open then lower bike in rear feet 1st (like a wiener dog). secure the bag with tie wraps (or tape). Open 2nd bag and lower bike front end 1st into bag; secure. If theres 'nekkid' space in the middle use an un-opened bag to wrap it.

Sometimes you can get the really big, very tough construction clean-up bags at the hardware stores. I can fit my whole bike in one of those.