Hi Gail,
for ease of discussion, please refer to the user manual (can be found at
www.bosch-diy.com).
Firstly, I assume that the depth stop ( item 11 in the drawings) is free to move, ie the wing boltt (11) holding it in place is loose . You can remove the stop when in the table, it will tend to fall ou anway.
Secondly, that model self-locks the cutting height when the spring-loaded clamping lever (16) is released. The clamping lever is situated at the rear left-hand side of the body, accessible to your left thumb when using the router in hand-held mode. Normally, one pulls the lever towards the handle, plunges the router to the desired depth, then releases the handle to lock the depth until the cut is completed.
For what you are trying to do, you either have to reach under the table to yank on the clamping lever, or disable the clamping mechanism, or somehow bind the lever in the unlocked position. It sounds like you have figured out how to keep the power switch on when the router is table-mounted, perhaps a similar approach will allow you to defeat the auto-depth lock. The lock is actually in some ways desirable, but since you will be using a scissor-lift, it is not necessary in table-mounted use.
You will still have some resistance to lifting from the springs inside the rubber dust boots. Your scissor lift should be able to overcome the resistance easily, but if necessary, the springs can be removed (painful to re-install if you subsequently want to use the machine hand-held). Just make sure the whole mounting plate - cum - router cannot be physically lifted out of the table.
Some points about the scissor lift:
1. As mgmine says, a car jack has too coarse a mechanism.
2. There are some lifts designed for this purpose. In general, it is better to creep up on the bit height, so the whole system is under compression. If you overshoot, drop back don to below the correct height and creep up again. The machine may not drop fully, if you try to just wind down the lift.
3. That machine has air intake holes at the top of the body (in handheld mode). Make sure that you do not cover them with the plate of the scissor lift. You may need some sort of spacer to ensure air flow.
Good luck with your endevours.