I've not used the shockmount, but seen it, so forgive me if I'm a bit out of line...
I think you can use the 8415 by, rather than inserting bar through it normally, pull the right band to the left, and left to the right and put bar into the mount that way. It will create much more tension than sliding it through without crossing the bands. That is the method used by similar looking (to me) devices, such as the tensimount shocks.
If you are already doing this, or it is just not feasible, just smack me.
hmmm
goose