Have you used the circuits as presented in the Tony van Roon article? Any problems?
Several years ago I used the CD4069 to buffer some servo signals. Worked fine for me. I have no doubt that it will cheerfully restore operation on your ganged Hitec digitals.
Be sure to build it to withstand the rigors of the model aircraft environment. Do not under estimate the harsh vibration levels that some models exhibit. Do NOT use a socket on the IC (as tempting as it may be). If building circuits like this is not your cup of tea then run down to the RC hobby store and buy a factory made solution.
Do you know if this circuit is essentially what you get when you buy a buffered extension or Y?
There are several designs out there. This is just one low cost way to do it.