I've tried this and it seems to work!
I have to place these .gpx files in a directory where I can find them with the (in Dutch) 'bestanden' app and then I can send them to the Drive app and then that app will send the .gpx files to my ZUMO XT.
Thanks for the tip!
If the above means you are using an iPad then use the Chrome Browser.
This will allow you to simply download the GPX Beta XT file and then once it it downloaded it will automatically give you the “Open In” prompt where you can select the Garmin Drive App.
If the Drive App is not showing the first time you do this select “More” and choose the Drive App.
It will then always be available.
Safari will force you to save the file to a location and will not give you the prompt to “Open In”.
Therefore you have to go looking for the file.