I have had one-on-one discussions with ATC supervisors about the
possibilities of cloud flights and came away with the impression that they
(ATC) would do all they could to make such flights possible - if you played
by their rules.

Not very likely to be able to follow ATC's rules. You have to be on an
instrument flight plan and ATC would expect you to hold heading and altitude.
You also would have to be transponder equiped. ATC will work with you and it
is possible to educate them of your needs but they are not used to gliders and
if other traffic is in the area ATC is not likely to let you not hold heading
and alt.