Someone asked for this on reddit, I couldn't find anything online so I made it myself since I have the XCEL 100s. They should fit the XCEL 500s as they are the exact same everything except the 500s have bluetooth.

If it seems a bit tight, make sure to check your dimensions and if they are all good, then push a bit harder than you think you would want to and it will snap on.

Added some grooves to the side to get better grip when removing it.