Here is what I have setup on my system using WideFS and the CH Flight Sim Yoke. I have the left trigger button for COM Channels and I have the right trigger for Private Channels.
FSUIPC
[buttons]
1=R0,0,C1006,1
2=U0,0,C1006,2
3=R0,1,C1006,3
4=U0,1,C1006,4
WIDECLIENT
[user]
Log=Errors+
ActionKeys=Yes
UseSendInput=Yes
KeySend1=RWon
KeySend2=RWoff
KeySend3=144,16 ; Press Numlock
KeySend4=144,24 ; Release Numlock
On the #3 and #4 options, I use the Numlock Key. You can use what ever key you want. I also have Numlock set for my PVT Channel in SB3.
First program FSUIPC with the buttons you want to use. Make sure you select the Keysend FSUIPC 1-225 option in the menu. Your first button will be #1 and #2, your second button will be #3 and #4. Then all you have to do is setup Wideclient with the key you want to use on #3 and #4. I hope this helps.