A simple method is to tie the dinghy
rings to the blocks via a long lanyard which has an eye splice in one end of it. A tucked sheet bend secures a loop from the eye splice through the dinghy
loop ond the block. When the dinghy is lowered in to the water
, you give the lanyard a tug and the sheet bend opens allowing the block to dinghy ring tether to come adrift. One then pulls the boat around to the boarding platform or wherever by a painter which is tied off to the taffrail before the vessel is hoisted.
One can also buy hinged shackles with a pull-release mechanism--but I hate spending beer