Does it see the SDR as one satellite, or multiple? I guess you can just spoof as many satellites as you want, but wouldn't it be rather hard to spoof a position?
Not the OP, but it'd see it as multiple SVs. Basically you figure out what the range would be from the SVs to whatever location you want the things to think they're at, and put out all the signals to make that happen. Spoofing a single SV is pretty useless, you have to spoof at least enough of them to give you a position solution.