Bump. From the terminal, I see no reason why this shouldn't work. I've mounted with the same options as other partitions, and even used chmod and chown to modify permissions to be identical to those in other mounts. I'm not sure if this is a KitKat issue, or something HTC has done to the ROM itself.
I've been able to do this on both my Incredible and Rezound, both with stock and AOSP ROMs. I'm really stumped why I can't get this working on my M8.
Motorola Q Black
Samsung Omnia SCH-i910 w/Adrynalyne's WM-6.1 v1.6
HTC Incredible ADR6300VW2 [S-Off] w/ CyanogenMod 7 & IncrediKernel
Samsung Galaxy Nexus [returned]
HTC Rezound ADR6425LVW [S-Off] w/ Beanstalk and Hiro Kernel.
HTC One M7 HTC6500LVW [S-Off] [sold}
HTC One M8 HTC6525LVW [S-Off]
Kein Mitleid Für Die Mehrheit!