Uh, onewasp,
Mode I is elevator and rudder on the left stick, throttle and ailerons on the right stick. It has nothing to do with thumb placement.

geish,
Place your thumbs wherever you find it most comfortable. Personally, I've always found it easier to fly with thumb and index finger. I feel I have more control that way. Try this; hold a pen or pencil point down on a table top; try moving the top in circles of ever larger diameter while keeping the point in the same place. Try it first with just your thumb, then try it with thumb and finger holding it lightly.

Anyway, we're all different so do what works for you.

CaffeenMan,
I hold the transmitter with three fingers of each hand, the sticks with index finger and thumb. Use a neck strap, but no tray.

Rick,
Why in God's name would a club care which Mode you fly?? [&:]
Dennis-