I have used the AT853rx, Audix 1290 mics, and the SMT-MICRO mounts (headed Cliff's way), so I'll throw in my 2 cents.
If you use the AT853rx with the Audix SMT-MICRO on a vert bar, you can only do XY. Using this mic/shockmount combo on a t-bar instead would probably allow all the other normal configs, DIN, ORTF, NOS.
If you are using the AT8434 mic mounts that comes with the genuine AT853rx, then you can use those with the Shure A27M vert bar to do NOS, DIN, and ORTF, but not XY. Of course, you'll get no shock protection.
If you cut down the AT8434 mic mounts, they would fit into the SMT-MICRO and allow you to do other configs. Cost starts to add up if you don't already have a pair of AT8434.
Here's what has worked best for me when using both the AT853rx and Audix 1290. I made up a miniature vert bar, attached the mics, and placed this assembly into a single AT8410a shockmount. Not as small a footprint as I got with the Audix mounts, but better shock protection. Can do DIN, ORTF, and XY with this setup. Someday I'll post some plans for the mini vert bar. Not too hard or expensive to make.
Otherwise, morganhalton's windscreen/shockmount idea also sounds like it might work if you use a t-bar. Finally, if there's a problem with vertical spacing and near-coincident configs, I've not heard about it. If you use a vert bar, there'll always be vertical spacing.