If back alignment can be maintained but the risk is the sustained upper back flexion when positioned over arm support
Sit with back aligned and supported, use two dumbbells or theraband.
If a client could do this (strength and control wise) then it may be OK to continue. Watch transitions onto/off of bar. Use of gravitron to offset body weight. Care in transitions in and out of machine.
The typical biceps stretch shown above is more of a chest stretch and often incorporates twisting which should be avoided.