Control lines through deck

[Brian Duff]

I would think that bringing the b/s lead below deck with a suitable deck block placed so that some cover can be provided by a folding seat, or perhaps a clamshell vent or even a piece of structure, shaped to keep rain water from running into it. That would be enough for inshore use.
Off shore use, just lead the lines below deck and out again with either upright deck blocks or thru-deck blocks, and box them in to drain overboard ( or cut a channel and cover it with a deck plate and screws) .
You might also consider trying, as you mentioned, a piece of hard rubber with a X/16" in it hold installed over the thru-deck block, that may work well. Watch how the angle will change as the height of you bridle block changes, make sure what ever you build leads fair and still does its job of keeping the bulk of water out.
Have fun !