One simple trick I use (which can be used on any app) is to make myself a permanent part of the solution. For instance, on W&B Pro (that's the one I linked to above) I can enter my weight & station and make it a "hidden" field that doesn't need to be updated each time. I just use the slider for the copilot's weight. After all, if I'm computing a W&B I know exactly who's in the front left seat.
Sure, I vary by 5-10 lbs seasonally but it's close enough.
