Here in southern Florida, when the usual chain-hanging ornamental "balls" of staghorns fall from trees, they readily split apart, and you can nab the younger, movable "shields" and tie/liquid nail them to tree trunks, especially in the rainy season.

I think that is your key--if you are mounting on wood crate, you can saw off a shield and mount it to the board. Then tuck sphagnum moss around that shield's base to help retain moisture. Then, the key is bright light (no direct sun unless it is an hour at sunrise or sunset) and high humidity, moisture which will promote new roots and eventual attachment to the crate.

By mounting the shield to the wood, I think, if I understand your concern, there will be less of a protrusion of the clump out from the wood surface. As long as you leave a fair amount of brown root mat (2-4" thick) behind the shield, there should be ample root there to pamper and get the plant off to a good start.

Hi
Personally I like like them stickinng away from the board in a half circle This allows the fronds to come out in several directions. It will eventually flaten anyway.
I wouldn't remove any root at all it will attach much faster and grow better. Be sure to keep it in the shade and as humid as possible
Another interesting way to do them is mounted on the outside of a wire basket filled with shagnum.They quickly develop into a ball.
gary

Thanks for the suggestions. I think I'm going to try to mount it to the outside of the wire basket.

Here is a link that might be useful: my staghorn

I've a question..I once tried mounting a staghorn, but living in IL, it was difficult keeping and died..
Is there a certain way to keep this plant moist? How does one water? I have a staghorn now, but it's growing in a pot. Oh and how about feeding? Thanks, Toni

using a wrapping of or a hanging basket of sphagnum moss is a start.

You can drench the staghorn like you'd water an orchid--rainfall wets the plant and it trickles into the roots, fast drainage is required.

An seasonal weakened formula of a 10-10-10 to the fern is how you'd fertilize. Since you're so far north, I suspect once to twice a year (say, early summer and then mid Sept before the cooler days set in) would be ok.

Staghorns like humidity but not to have their roots (remain) wet. You can get a little rough with the potted one - cut through the clump and spread it out a little so it won't stick out so far on whatever surface you mount it on.