You will already have a flow restrictor and the pipe exiting the membrane.
You could try fitting a push fit inline tap so that you can manually adjust pure/waste ratio.
But really you won't achieve the same rate you will getting before with no pump.
I've got an old 400 gpd Vyair RO in the garage which I don't use anymore.
If you can find out the exact pump you have, maybe model number etc. I will look to see if my one is same or similar.
If it's any good you can have it for free if you want but you will have to pay postage.