You can't do it directly in Motion, but you can create an Application keyboard shortcut in System Preferences > Keyboard.
Open the Keyboard sysPref pane and click on the Shortcuts "tab".
Select the App Shortcuts in the sidebar.
Click the + button under view panes.
In the dialog that shows up, select Motion from the Application menu.
In order for the shortcut to work, you have to provide the *exact* case-sensitive menu label you want this shortcut tool to use. In this case it is:
Export using Compressor Settings...
(that's 3 periods on the end - not that 'using' is all lowercase.)
Provide the shortcut you want to use. I set up Control-Shift-e in this example:
Then, when you're in Motion (and only in Motion) when you type the shortcut you set up, you will go directly to the Export dialog.
HTH