Could you explain a little more about your 910xt mount? I purchased one this summer, and have been wondering how I could mount it on and off the bike quickly during triathlon races.
First of all you need to buy the Garmin "bike mount". It contains a new strap, and a quick mount that you attach to the watch in stead of the existing strap, and 2 x mounts to attach on the stem of your bike. This enables the possibility of snapping of the 910XT unit in a quarter turn motion. The strap stays on your wrist, and the 910XT unit is now able to be attached to the mount on the stem. When reaching T2 you snap the 910XT unit of the stem and back on the wrist... and of you go
To avoid the plastic mount (attached with rubber bands) on your stem - not looking that integrated, and forces you to bend your head a little too much during biking - numerous companies have made a mount, that is attached to the handlebars, and puts your Garmin product out in front (and flush) of your stem. Most of them are for the Garmin 500/800. And for some reason Garmin have decided that the mount on their 910XT kit is turned 90 degrees compared to the 500/800. This makes your 910XT sit "sideways".... not really an option
However, Martyn from RWD (Race Ware Direct) has made a special mount, that fits the 910XT perfect... AND makes it sit right there in front of the stem.
Have a look at their website... og make a search here. There are lots of info on that product.