You should be able to get into your settings and:

PMIX1 - on (tells the computer you want to use a user 'p'rogrammed 'mix'
MAS - CH1 (sets the master channel to ch.1) or is it 2 for your radio - used to have it but I forget - my Airtronics has ch 1 for elevator
SLV - CH5 (Slaves channel 5 to master (1) )
PMIX - +/- 100 (this should 'reverse' the servo if need be using positive or negative)
SW - ON (means you don't need to activate the mix - it's always on).

You can use a 'Y' harness, and for general sport flying it should work fine. Like said above, if one servo is going the wrong way, have the control arms come to the top of one servo and the bottom of the other.