Cross-staff beaming with multiple instruments

If I'm working so as to have an audio export based on soundfonts, I've found that having multiple instruments for what would normally be one grand staff instrument gives me more control over the bass and treble's volume and pan settings in the mixer: i.e. instead of a grand staff, I have two separate piano instruments--one of treble and one of bass clef--and I stretch the brace to fit both so as to give the appearance of a grand staff while getting rid of the second brace. The only problem is that the ability for "cross-staff beaming" is no longer available, and it makes sense that it doesn't work anymore. Is there any possible way to get cross-staff beaming in this way of working? I haven't figured it out if so. This would allow the appearance of a true Grand Staff while providing the extra mixer controls for audio exporting.