You should be able to go to Home Depot and buy insulation and a machine to blow it in. You do not need to get up there in order to insulate. I have a similar problem. I have a small fan on the floor in front of the vent and turn it on when I am in there to pull more air from the duct/vent
I recently did that with my husband for a job. It's not all the expensive and the machine was a piece of cake to use. Note that you need two men to lift the maching, a 120# woman is pretty useless there.
You need to know where to build frames to vent the soffits but Home Depot is very good with that info.
The machines are incredible, and easy to use, the insulation comes in compacted bales that even I could lift. We insulated a 10,000 sq ft second story attic in 4 hours including picking up and returning the equipment and clean up.