I have seen cradles made of acrylic tubes cut lengthwise, supported by a smaller-diameter tube. A single cradle per lightsaber.
First hit on Google is a RPF post.If you google "MOM Liughtsaber stand" youll see what he means.
Lucasfilm had used a similar design at the "Magic of the Myth" exhibit. At other exhibits, Lucasfilm has also used stands like MR's and I think at one time short vertical acrylic tubes cut at an angle that the sabers have been stuck in vertically.I offered these MOM like stands about 5 years ago, some of which I made light up.
http://www.bothanjedi.com/gallery/d/3198-4/stand1.jpg
http://www.bothanjedi.com/gallery/d/1482-7/stand5.jpg
99% of the custom sabers out there use a 1" dia. blade. However one could make swappable rods for the display case that works with 7/8" and 3/4" dia. blades. Also, 99% of the custom sabers out there use a blade retention screw to hold the blade in. So again, not really that much of an issue, even if the blade retention screw is a flush mounted set screw. Just make sure the tube stays attached to the bottom base so that the cap with saber are easily installed/removed from it.
Back in the day, there used to be a custom saber business called Lightech Industries that made a vertical display case. Here's a pic of it...
http://www.starwars.idv.tw/communication/contribute/Weinziel/vault.jpg
I think it's pretty sweet looking and suspending the saber by the blade retention screw in the emitter is a nice touch.