Hardwiring shouldn't be a problem, all the bags are hardwired technically. It's the SRS unit that sends the 1-3A of current to deploy the bags.
Here's the problem I see: If you wire your single stage SRS unit to the 1st stage of the 2 stage bag, how much does that inflate it? Probably not enough. So, then you wire your single stage bag to BOTH stages of the airbag. What happens when both stage inflate the bag at the same time?
I'm not going to tell you to go do it or that it will work, I just don't know enough about how the SRS unit and airbag work and how precise the inflation has to be. All I'm really good for is figuring out what wires are there and which ones to connect.
A little wiki-research tells me that the first stage is for moderate crashes and the second stage is for severe crashes. So one or the other ignites, not both I would assume. So, wire up the the 2nd stage of the airbag for maximum protection in all crashes?