Video crossfading when using CDJ850's ???

Hi guys,,
Ive got bought the the Video Plug In,
At the moment I'm having to do the video crossfades using the mouse,
I'd like to know if there is a better way?
Is it possible to map any keys on the CDJ's (850's), I'm thinking this isn't possible as they are HID connected.
For example, it would be good to have the Reverse button as the video Cross fader button, no one uses reverse
Or any better ideas ?? maybe a separate MIDI controller ???
Thanks, Jeff.
Ive got bought the the Video Plug In,
At the moment I'm having to do the video crossfades using the mouse,
I'd like to know if there is a better way?
Is it possible to map any keys on the CDJ's (850's), I'm thinking this isn't possible as they are HID connected.
For example, it would be good to have the Reverse button as the video Cross fader button, no one uses reverse

Or any better ideas ?? maybe a separate MIDI controller ???
Thanks, Jeff.