Are you matrixing it with an AUD source? If so, it might not be that bad as you'll get a lot of wetness out of the AUD. If not, and you only have the SBD, you can try a bunch of things, but the times I've tried this, I've had mixed results and gone back to the mono source sometimes. Try a TINY amount of reverb. Try a TINY amount of delay in one channel (this one is my preferred method). Try a TINY bit of a "doubler" VST plugin (usually used for chorusing vocals). Sometimes the doublers have an ability to delay the signals to L and R differently, and sometimes they let you do some crazy stuff with real-time panning of the doubling, but it's WAY hit or miss. There are others, but you might want to try pasting the mono track into both channels of a stereo track, and then "slipping" one channel just a tiny bit to delay it from the other -- it doesn't take much. Watch out too because some crazy-ass biaural processing comes into play in your head once you delay the one side too far. You literally won't hear the delayed side anymore when listening in headphones, it's really weird, even though if you listen with one ear at a time, the full signal is coming through both sides of the headphones.