would you consider using Mitegen MicroRT instead of a capillary? In that case you can use adhesive mounts such as the Crystal Catcher by Kyodo. We used their kit for dehydration experiments at synchrotron and it mounted without damaging them all the type of crystals we tested. (refer to
http://journals.iucr.org/d/issues/2014/09/00/gm5033/gm5033.pdf)
It simply needs the crystal to be touched by a special glue mounted on their standard sized and then just cap it with the MicroRT.
Hope this helps.
Marco