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We're currently using Airwatch for our MDM.  I was not able to add the URL as a custom parameter, but I did find a good work around for us.  I deployed the Connectwise Control app to all devices a while back.  Next, I deployed a web shortcut to all iOS devices that points to our Control URL and called it "IT Help". 

When somebody calls for help with their iPad or iPhone, I tell them to click the "IT Help" icon on their home screen.  This directs them straight to our Control URL in Safari and asks for the 5 digit access code.  They then hit the arrow after putting in the code and it asks if they want to download Control or open the link in the Control app.

A cool thing I noticed is that it keeps the Control URL in their Control app once they go through the steps above.  I hope you guys can find this helpful.