I think right now the only way to do that is to run a DAW and select one side of one of the 828's stereo pairs as a mono output. You can only route like that with a DAW using the MOTU ins and outs as the i/o.
I'm doing this in a live situation (MOTU 828Mkiii and Nuendo 3), as well as running MIDI cue'd effects in real-time (only side chain fx, no inserts, as latency becomes annoying, even when buffered to very low.) I needed to have 2 mono outs for feeding floor wedges. The problem then becomes the fact that the 828 wants to send only to stereo pairs of outs, so your mono mix in the DAW is not a true mono mix, it's half of a stereo mix. Anything that is panned to the other side is missing or lower in level, or too high a level if panned to that side (like a lonely George Harrison vocal harmony on an old Beatles record - he said, showing his age). So you must do your mix in the DAW for these mixes, so that you have true mono mixes.
All that may have sounded convoluted and confusing, but I swear it had logical thought behind it.
But there are infinite advantages of using a DAW to augment CueMix FX in a live gig situation. One of which is finally having a mixer that shows a decent number of faders at once (since you can widen or narrow them in Nuendo) and has custom names on those channels, ins or outs (only Mac's OS will allow channel names editing, and I believe that's only with the inputs, not the outputs.) But the theory is that you set your mix levels up in CueMix, then set all levels in Nuendo to a common level, such as 0, -5, -10, etc. This way Nuendo only
tweaks the mixes on occasion. Then when you get into automating faders levels from song to song, as well as vocal effects, eq adjustments, drum reverbs and such, you start to see the power of this setup for a live band, particularly one as cheap as mine, wherein the last thing we want to do is pay a FOH guy for cover band gigs.
