One way to overcome the resolution problem would be to dedicate two inputs for the control of a single parameter and then mix the incoming signals using mixer units.
You would have one control for a coarse setting and then another one for fine grain control.
The coarse input would have enough gain to cover the full range of the parameter on the ER-301, the fine input would be attenuated so the entire range of 128 would only work over a much smaller division of the full range.
It might take some experimentation to get the balance right!
Edit: it may even pay to have three controls, the same principle could be applied repeatedly until you had enough!