Yes there is a trick to using the trax 2 wheels.
I had the same problem until I found out that if you twist the black hub knob
a quarter turn, this releases the wheel assembly from the axle.
with the "near side" wheel removed, it is easy to fit the cart with one hand, then you can just "click" the "near side" wheel back on.
Thanks, Montedane! Sounds like an excellent idea and can't wait to try that, (though the idea of weighting the wheels with a bit of water is also interesting).
Bob -- it's very hard to use two hands to insert the cart, because the winds and tides where I launch usually require one hand to hold the boat.