Okay, have to check something in the air, but playing around with the box 'o magic this morning in the hangar (SW V 802.4...no PPOS Hold LSK option).
There is a position hold LSK on Nav page 3. I will have to see if it allows you to save this as a user waypoint (I couldn't on the ground, but maybe in the air).
If you have two FMS, I would suggest using #2 to capture the lat long, make note of the aircraft track for inbound leg definition, then go to heading mode and do a 180. From there, go straight to holding definition on FMS #1 and type in some random name (I just typed USER1). If it doesn't already exist, you will be prompted to define it. Type in the lat long that you have held on FMS #2, and then set up the hold as you normally would.
I'll verify this in about 6 hours after I'm done today.