Best option for financing a short sale

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This is our first attempt at purchasing a short sale and are not sure what the best financing route would be. Property is a condo in NJ. It was listed on the MLS for about 6 months, then lien-holder said they were starting the process to short sale. We put in offer at list 400k and sellers accepted. They owe the bank 450k and HOA of $10k which we will cover. No other lien holders. Now just waiting for bank's answer. We realize the bank may or may not accept the offer. In the meantime we need to come up with a commitment letter in 30 days. We want to limit what we may forfeit in up-front monies in case the deal doesn't close. We plan on 40% down and finance the rest. Should we:

• Refi our primary residence - if so, how do we time this with an unsure closing?
• HELOC now then refi the HELOC after closing? What are the risks?
• HELOC for now and try to get refi if lien holder accepts - possible to get it before closing?
• Mortgage as second home?

Other considerations... we have a primary residence with about 360k equity; we own 3.5 investment properties, all with positive cash flow IF depreciation is backed out. Do we need to worry about qualifying for any of the financing options? We don't want to get stuck in a HELOC for more than a few months.