The discs are only mechanical if that makes a difference.
I consulted at the weekend with the LBS owner who facilitated my acts of whimsy about this and we looked at fitting bar end shifters or sti levers, but it would cost over £100 and I think that money would be better put towards my next bike.
... although I could get some second hand myself ...
Please tell me more about these '90 degree banjo connectors', though.