I was able to use the Nano cushion with the Swift FX head gear without any stability issues.
But then other than very minor back strap slipping on occasion, I never had any issue with the Swift FX moving around much either
The pillows didn't move and when I tried the Nano cushion it didn't move either so I haven't thought about what might be used to help keep the Nano cushion from moving around. I would think it wouldn't move much unless the fit was less than optimal if the back strap wasn't the culprit.
I suppose someone could try some sort of homemade TShirt material liner just to get an idea. I have never used a mask other than a nasal pillow mask and the brief time with the Nano...so I am zero help when it comes to liners other than to suggest that someone give it a try to see if it helps.