There will be a few options, I'm sure. Those of us with carbon
fuselages will need to experiment.
My OzFLARM Nimbus 3 install (now back in the USA and part of Steve
Leonard's fleet) had a high-gain film antenna stuck to the inside of
the canopy. It looks obvious from the outside but was not visible to
the pilot in flight. These were for sale by the original manufacturer
of the OzFLARM, Nigel Andrews at RF Developments. I have not seen
those antennas on the Swift Avionics (current Australian FLARM
representative) website.
Of course this was a top-of-the-panel mount with an internal GPS
antenna and didn't need a transponder antenna. Before installing the
high-gain antenna, I took the plastic cover off the standard OzFLARM
antenna and replaced it with clear instrument tubing - less obtrusive
than the black stick.
There are a few antenna options for the standard FLARM shown on this
page:
http://www.swiftavionics.com.au/prod.../1/Sailplanes/
The suction cup mount antenna (just above Altair Pro) and similar GPS
antenna mounts may be a good way to experiment with placement.
Whilst you're on the Swift website, look at their FLARMNAV. Makes a
simple package for club gliders.
Jim