Hi Bill,
Consider using a wire segment in the mizzen top'n' lift. A rope connection (or splice) at the top, around the sheave and drop to deck for adjustment. The lower end is also insulated (via rope?) to the boom and the antennea lead is fixed to the lower end of the wire.
Alternatively you could dead-end the upper end and have the adjustment lead at the lower end to save a bit o' weight aloft.
I believe you will have better radio performance with the antennea more vertical.
How about trying one of these gizmos and report back to us:
http://www.splicingnut.com/
I have no affiliation to splicing nut (but maybe I are one).
Cheers, Russ L