Ok this might be an odd request but is there a way to block access to a Horizon UAG from mobile phones?

Here is the scenario that recently happened and prompted management to ask me to find a solution:

User is late for work. They install Horizon app on their mobile device and access their VM so they can punch in on the internal clock website on time. Then user shows up late and gets busted by management for coming in late. 

They check the time clock and ask how the user clocked in before actually arriving. User admits to what they did using their phone.

Long story short, is there any way we can block remote access from mobile phones or whitelist specific hardware? It's not something I want to deal with but this is apparently a big problem at this specific site.

Currently we are working towards implementing Instant Clones and DEM but these users are still on a linked clone environment. All outside access is routed through a UAG. Internal access goes directly to the connection server.

Love to hear any ideas you folks might have.