As the OP points out, there are two separate objectives. One is to be
able to release quickly while the other is to not release
accidently.

Attaching the release cable to your hand has the potential to slightly
quicken the release action but in doing so, you are greatly
compromising the second goal. Since we're offering 2 cent advise
here, I'll advise against doing that. If you hit a big bump or
scratch your nose or open the vent or tighten your straps, bingo! your
headed down. This seems like a bad idea.

I would also point out that adding an extra link to the tow release is
essentially changing the design of your glider. Many pilots are not
qualified to make such a design change. A strap may seem like a
simple device, but there are an awful lot of ways for that added strap
to not work when it's needed. This is made worse by the fact that it
will be rarely tested.

I think the best bet is to simply position your hand within a couple
inches of the release. As you sit in the cockpit waiting for tow,
practice making the quick grab while you are mentally preparing
yourself in terms of the particular circumstances that will drive that
action. I don't beleive there is any reason to worry about grabbing
the tow release and the dive brake at the same time, the tow release
is always first.

GW