(sigh) unfortunately I have yet to find a way to do either of these...
I would love to put the entire 3cx folder on, say, the D: drive - or hey, even just a few of the folders that have content that can grow - voicemails, provisioning files, firmware, etc - but alas, I haven't seen a way yet.
I 'sppose you could mount a disk for those folders - Windows/NTFS does support that now - and that would allow you to put it on a SAN or something - or even just a different disk - but I haven't found any way to actually relocate them out of C:\ProgramData\3cx*.