You don't have to move the lens out of the way for 1.85:1 since you can use a video processor (or possibly your projector/amplifier/player to scale the image to 'horizontal squeeze' so that you get the 1.85:1 image with black bars each side of your 2.35:1 screen.
However, this means that you'll be watching an image of approx 1400 x 1080 pixels so you'll be wasting some of the pixels and of course scaling the 1.85:1 image.
If you move the lens out of the way, you can use your lens memory to slightly zoom the image so that the screen height is filled (you'll still have side bars, but these won't be 'created' by your projector's best black level, they will be unlit sections of the screen.
This is what I do with my JVC X35 and Isco II lens: I have a 2.35:1 memory setting for when the lens is in place (minimum zoom in my case). Then another 1.85:1 setting which applies a little zoom and tiny amount of horizontal shift to realign the image. I just decide before watching the film if I need to place my lens in front of the projector (mine is on a fixed stand). I can use my video processor (Lumagen Mini3D) to instantly change the aspect ratio (as above, so losing some pixels) for menus and trailers before the main 2.35:1 feature starts.
Zooming: Been there, done that, bought the lens...