A 401k loan is a much better plan than a 401k withdrawal, see if you can do that. Most companies with 401k do allow the loan, you just pay yourself 3.5%, and it is repaid through your paycheck over a time period of your choice. (up to 5 years, though you can pay it back faster without penalty)
If not, then I suggest trying to short sell using other money than cash out of 401k. I definitely agree with the idea of the short sell right away rather than waiting, especially if you have a few offers and don't think the price will go up.