Options
1 - Run a stage rig, THRU THE SNAKE. Setup your mic's onstage, and get them to patch them into the snake running back to the FOH mix, then blend them with the full mix-out of the SBD - this would require an outboard mixer.
2 - If the FOH is not to far from the stage, run a pair of mic's at the mix position, blended with the feed from the sbd - this also would require an outboard mixer.
3 - Run 2 separate rigs - one for the mic's, one for the sbd - and blend/mix them in post using one of the many audio programs available for this purpose. Drawbacks: having to have/run 2 seperate rigs and synch the 2 recordings (especially if they are 2 different A/D's, as 2 different clocks will mean having to make sure everything is still in synch every so often).
4 - Beg, borrow or steal a SD744T and do either (1) or (2) above...
Rick