since you are feeding the high protein grain, I would think it would be fine to give the poorer quality hay. You mentioned that you were only going to do this for a little while and I would think that would be fine.
You could try fencing them in a small area of your pasture, where they can't get enough fresh grass to give themselves bloat, then provide slightly less of the creep feed.
Last summer I had my lambs out on pasture from day 1, but in a 5'x12' pen, and I gave them 1/4 of the recommended amount of grain. I moved the pen multiple times a day, like a sheep tractor. They did grow slightly slower, but they also never bloated. Then, you could continue to work with them in a small space.
HI -- I am new to sheep and I just got two, a 4 month old ewe, 1/2 Suffolk, 1/2 Babydoll and a wether Babydoll. I have they both in a paddock with restricted access to the pasture and I am feeding lamb grower and all stock sweet feed. I am not sure how MUCH to be feeding though. They have free access to hay and limited pasture right now as well. I give them each about .5 lbs of feed mixed together twice a day. I know the breeder wasn't feeding any pellet except occasional sweet feed as a treat or enticement. They also have unrestricted access to sheep mineral, but aren't very interested in it. Any suggestions?