Oh, I wish we had one, too.
I simply do them by lying prone on an adjustable bench set at the lowest inclined position.
It would be great to have the actual bench, but this method comes close enough to be the next best thing.
If you like curling from an elevated elbows position, also consider doing high-cable brachial curls. The tension is slightly different, and I do these every now and then to change things up.
I've also done cable curls on a lat pull down machine (curling the bar to behind my head), but the motion is rather awkward & uncomfortable for me.