I started to think you'd have to replace a mount, even if not totally accurate still should give useful data, surprised no one sells mounts like that.
This guy got an interesting way of getting a tq curve, with a tach, lev o gage and a camera to record the curve and with a peak tq guesstimate should be able to figure out a close dyno graph.
Technically speaking, a torque strap could do it, but the setup would have to be careful. When a mount takes up any force, it can distort the load measured by the cell and give an error.
Plenty of ways torque could be backed out of acceleration, and so long as there's no tire slip it will be fairly accurate.