As Terranaut has stated, going a few weeks with out eating is not an issue with Boas.
Be sure first to make sure your husbandry is on.
90-95 warm side.
75-80 cool side (I would never let the cool side run below 75deg).
Ambient temperature of 83-85deg.
50-60% humidity.
Having hides and at least three walls covered to make the snake feel secure will help as well.
Also having a light for day/night cycle is recommended, 12 on 12 off or there abouts.
One thing that I have found that works well for me is to increase the heat on the warm side. My temps normally run around 90-93 deg on the warm side. You can increase the temps to 95-96 deg on your warm side (make sure you can still maintain 80 deg on your cool side though). Keep it like this for approx., a week. After that get a Rubbermaid or sterilite tube, place the rat and snake in it a leave it for a couple hours covered with a towel.
If you are using live food (I don't recommend) you will have to check in on the snake more often. You don't want your snake to be harmed by the rat.
Hope this helps.