Fixing underdone pasta after adding sauce -- need answer fast

I just made a pot of shells with homemade cheese sauce for my daughter. I cooked the pasta for the longer time range indicated on the box, but apparently that wasn’t enough, as it’s still a hair short of al dente–still crunchy in the middle. Unfortunately, I didn’t realize this until I’d already drained it and mixed it in with the cheese sauce. Is there anything I can do to soften the pasta now, or am I sunk?

Add a little milk, cover it and bake it in the oven or simmered on the stove top.

Nuke it.

Well? What did you do, and did it work?

I nuked a small portion at first, and got it soft enough for her to eat. Tried the milk trick the next day, and it turned out okay, although the sauce got a little grainier.