Authorize.net and Sim and GMT Time

I got the following code from authorize.net for creating a timestamp that gets submitted with their SIM method. The problem is I need this to be in GMT time, I am on the east coast so is the server:

<cfset timestamp=DateDiff("s", "January 1 1970 00:00", DateConvert('local2UTC', Now())) >

Does anyone know how to convert this to GMT time.

Thanks

TJ