Nick, The drawback with the std fairlead/clamcleat is that the clamcleat takes quite load – and as you say is difficult to release.
A common solution is to use a swivel jammer in conjunction with a turning block. The turning block is usually ratchet.
The turning block in this photo is out of sight under the side deck. Because the turning block takes much of the load it is much easier to release the sheet at the jammer.
And if the crew is occupied it is a simple matter for the helm to trim the sheet at the swivel jammer.
Hope that helps