I once had a similar problem on two different occasions: one was fitting my ICD AdSpeed 14mhz 68k to the A500 I had at the time, the other was fitting a VESA video card in to a PC (those were ancient times!)
What I ended up doing in both cases was removing the system board from the case and placing it on the table, on top of a large nonconductive "pad" made out of four neoprene mousepads arranged in a square.
This gives cushion to the board with a firmness underneath to allow the card (or in one case, chip) to be firmly driven home.
It hasn't happened since, so I've had no reason to replicate that "workstation".
