This link might provide some ideas or inspiration (hopefully)…
But I agree with others - for changing the usable depth of the LR3, adding some boards under the Y rail and rollers would be easier, cheaper, and more likely to result in a flat cutting surface.
However easier and cheaper isn’t always the goal, so if you are thinking of a lift system, how about lifting the outside edges of the table that support the Y rail and rollers? That would provide an infinitely variable table depth along the entire table top. The devil would be making sure that all four actuators lifted or retracted the exact same amount. .