Wow, thank-you for the many helpful replies!! I realized upon reading
some of the replies that I left out some information.

I live in a community with strict covenants. ANY permanent changes
visible outside of the house require permission (I can't even cut down
a tree without obtaining approval). For that reason, some of the more
novel ideas (like the clothes-line trolley) might not be workable since
I know I would never be able to get it approved. Even the amount of
improvement of the path to the lake is limited because the community
wants to maintain the "natural look".
(PS I hate covenants like this, but that's a different issue!)

The idea about the buried hose running to a properly valved outlet on
the dock does sound convenient, but I'm not sure what are the
applicable regulations dealing with burying hose for gasoline in one's
yard. Does anyone has a pointer as to where I might look for
information on this? Somehow I have my doubts that it'd be simple to
do this in a legal way.

Also, there is no gas available on this lake (it is a small lake).

I do particularly like Tony Thomas's idea about the fuel pump. This is
something I'll consider. So long as I can ensure that I pump less fuel
than the boat will hold (i.e. with room to spare), I feel this could be
done safely and with minimal risk of spillage. I do wonder how long
this will take (i.e. what kind of flow rate I can expect). I guess I
might need to get some sort of rigid pipe to shove into the fuel tank
because the fuel filler has one of those little flaps that I think
might interfere with shoving a piece of hose into the tank.

Regarding the idea of the tank with the valve on the bottom ... heck, I
wonder if it might be possible for me to install some sort of valve
into my existing gas tank. Some aircraft engines have valves at the
bottom to be used to drain the oil during an oil change, I'd think that
has to be a pretty reliable valve (to prevent an oil leak in flight!!).
If I put the valve part of the way up the tank, then I could let it
run until it stopped (after ensuring more than adequate space available
in the boat tank) and still know that I had some gas in the Jeep to get
me back to the station.