I'd by some nice sliced chicken at the deli counter, stick it in a wee dish with gravy, cover with foil and cook for about 20 minutes while the beef is resting and you are sorting out your veggies. I do that every Christmas for my youngest as we like to have Duck and he wont touch it. If you want to be mega prepared, you could pre cook your beef as well and slice it when cold and put it in a dish and cover with gravy and heat up in the oven when you need it - that way, if it is a little tough, you can cooked it slowly in the gravy and it should tenderise a bit.