Midi Pad Presets

Is it possible to key specific presets to midi pads so they can be recalled in a non sequential order?

Yes, sending Program Change messages will select different Scenes (presets).
From the manual:

Program Change Messages

Program change messages received by ETC switch to the scene specified by the message’s value. So if a program change message with a value of 1 is received, ETC will switch to its first stored scene, and a program change message with value 4 would switch to the fourth scene, etc.

If no scenes are stored on ETC, then these program change messages will similarly map to the loaded modes. So a program change message with value 1 would switch to the first mode, 9 to the ninth mode, etc.