Credits goes to Peter Cheuk and B100.
First, when installing the rear passenger side shock on A4. The rear bolt is hard to get in the right direction. So if you want to play it safe, remove the fender liner and install it like this:
Now the front part, first remove the top nut. Peter improvise a tool, basically take a 19mm socket and gring the two side a little, so a wrench can hold it tight.
Now the passenger side, the idea is:
You don't have to drop the subframe if you can compress the spring on the car. Since the hub on the passenger side is hard to lower, we have the compress the spring really hard.
Also the sway bar prevent the passenger side dropping to far, we disconnect it first. Notice how we use the spreader tool in the picture.
Then we use jack to lift up the hub and use spring compressors to hold the spring. Notice the nut end of the compressor is on top. Tighten them by bare hand.
We need to get the spring compressed REALLY HARD.
Then lower the lift, we have enough (just barely) space to get the strut out. Before put the new strut back, we compress the spring even harder to make the installation easier.
btw, the new rubber mount seems a little bit high than the stock.