How does an eBow unit work?
I guess it keeps the string vibrating somehow.
Could you modify it and do the pinch harmonics thingy to get that feedback feel?????
Or could you create an internal loopback in Reaper and have some delays and limiters/compressors and stuff keeping it slower in changes?
There is some setting in Reaper if to allow feedback in routing(project settings).
Then use JS/MIDI plugin controlled by expression pedal to adjust feedback amount.
There are some pedals with hold function, which is probably easier to get working properly though.
Some kind of whammy or distortion pedal, if I remember right.