Velvet masking without backing/support?

If you Hemmed all 4 edges, and sew on several or one complete strip of velcro on two opposing edges....it's probably do-able.

But if the masking is horizontal, stretching across a 120" width, the pull required will be pretty stiff.

Additional securing might be required along the horizontal edge at top & bottom to offset / prevent any sagging of those edges.

...............but why ask me, I just like to post.

A straight edge to the masking is critical. It seems to me it'd be difficult at best without more support across that kind of length. Maybe consider a metal bar insert where the velvet is hemmed around it. I know that's how a lot of the guys with the automatic systems that unroll the fabric off a rod do it.

But then again, I'm the kind of guy who can't stand even bumps from the fabric at the line of masking that meets the picture edge. Flat and straight is the rule for me.

A cord that runs through the Hem that lies "inward" to the image, and that is attached at each side with small, Black Painted Cleats would accomplish providing a very straight edge.

Like that is an obstacle? From the very beginning, hemming your edges was "Mandatory", not an option. Simply get your measurements and material in hand and get an estimate from a Fabric Shop or Seamstress who can do the sewing. I can assure you such a simple job isn't going to cost you as much as the BV did, and it makes everything your wishing to do possible.

Without such, really...your plans would all be for naught.

......unless.....you can find some "Iron-On Hem Tape". That stuff can work, but with a "soft nap" oriented fabric like Velvet, you had better be careful and follow directions to the letter, keeping both heat and pressure, as well as contact to a minimum to avoid any flattening or glossiness of the velvet.