Boyan,
Silver Solder a collar near to the top of the needle, use a fitting like a hollow brake pipe nut to clamp the collar into the mounting block whilst allowing the top of the needle and wire to show above the nut.
Silver solder a small block to the top of the wire, power can then be connected quickly and the tips can be swapped out quickly and easily,
Regards,
Nick

It's not an idea, more of a design description, with the right implementation it will definitely work ;-)