Pay Pal API Module - Interesting problem with signature

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Greetings all,
I have been happily using my first prestashop installation and have been amazed at the speed and ease with which the problems are solved, the customizations made and how robust the system is. However, only hours from launch I ran into a wall. I was hooking up the Pay Pal API module and the system asks for a signature. I ran in circles for an hour before I realized that my other store, a store that was custom built in 2005 uses a certificate or a cert_key_pem.txt file (generated by Pay Pal API credentials wizard) instead of a signature. I called Pay Pal and was informed I can only have one or the other, not both. Therefore I have quite a quandry, since there is no way I am going to retro engineer that old code to use the more modern system. I can still get a certificate from Pay Pal but not a certificate and a signature. The older site is still running and making money and is best left alone till it eventually gets an upgrade.
So what are my options? The Pay Pal API module would work, if I could supply that certificate instead of a signature. Another option I could use would be Pay Flow Pro, but I have been unable to find a Pay Flow pro module for prestashop. Any advise would be welcome, I was almost done till I ran into this problem.