As the law already makes the customer responsible for the use of the facsimile signature, I suggest you refrain from calling it an agreement - his agreement isn't necessary, it's just the way things are. Call it a disclosure.
Before you take this step, look at your signature card. It's pretty common that modern signature cards address facsimile signatures. If you feel its necessary to enhance any language you find there, be certain the language in your separate disclosure is consistent with that in the contract.
_________________________
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.