Health and Safety says NO.
The safest way of using a ladder is with 3 points of contact. You can't do the with two hands on a pole.
However, the boys at BT and Sky have a solution which you maybe able to copy. They have a need to be up a ladder and drill holes in walls. Using a rotary hammer drill requires 2 hands.
I spoke to a Sky installer once and watched him fit a dish. They drill an anchor point into the wall and secure their ladders to that. Then they use a full body harness which has a safety lanyard clipped onto the front of their harness (not the back) and to their ladder. They are then able to leant back as the safety harness is their third point of contact. Fitting an anchor point in the wall was part of fitting a Sky dish - no anchor, no dish, he told me.
There is a cleaner in our area who takes a chance and does them off ladders, but he will not do them unless he has someone to foot the ladders. He said he wasn't totally comfortable doing them that way.
Me. I would rather pass on the request - I have enough window cleaning work tbh.