How to bypass the issue and still ride the disc:
Requires 2 'disc casting magic-users...
Hop on each others discs. One directs his disc to stay 4' ahead, the other 4' behind. The lead mage then moves on the disc, causing his disc to move, causing the other disc to move, causing a rapid (your base move) movement of the discs in the direction the lead mage has moved.
Too confusing? Try this...
Mage A (MA) cast's his 'disc (DA)
Mage B (MB) cast's his 'disc (DB)
MA directs his disc to precede him at 5'
MB directs his disc to follow him at 5'
MB hops onto DA
MA hops ont DB
MB moves forward on his disc. DB moves to follow him. As DB moves to stay 5' behind MB, DA moves to stay 5' in front of MA.
You can even turn, etc. by shifting in a direction on the lead disc.
At moderate levels, you could even have a chain of paired wizards on discs parading around.
Hmm.
I think I'll have to use that
This use is 100% consistent with the RAW with no interp required, right?