No experience to date, but I'll be interested to hear how you get on, since one of our consultants wants to use a HFOV on retrieval, and I don't see how that will work with just an HME!
I'd wondered about the small 'home' humidifiers that some companies make to go with CPAP systems, as they tend to be smaller, lighter, easier to fix down and less liable to slosh water into the circuit when moved - but this is pure speculation and I haven't tried it!
Good luck, and please keep me posted!
Moira