[SeanMcK]

Refugee, there is a narrow groove in the plastic behind the linking terminals, in line with where the -ve connection should be but only solid plastic behind the other -ve terminal. I don't understand you idea for mobile phone contacts, sorry.
Phil, akin to the 4.5V battery terminals in an Avo 40, 7 etc.? Thinking on that.......hmmm, the gap to be taken up is rather tight, about 1/8th" or less, the bending shaping might be 'interesting'.
The current solution for the linking terminals is 3 6BA brass washers soldered together as a stack and to the terminal with a copper beryllium wave washer soldered to the 'top' of the stack to act as a spring.