I am not from Laminar Research; just a flight simmer from downunder.
Like you I also have XP10 and the USB dongle that substitutes for disc1 and the disc version of XP11.
I also read into your question that you have ascertained you cannot purchase a USB dongle for XP11. Laminar Research advised me some time back that a dongle is not available and is not on their current radar to do so.
XP10 is a totally different package to XP11. Neither software package will interact with the other. I strongly suggest you do not "stuff around" converting the XP10 USB dongle into a XP11 unit. Once you do you will not be able to use it with XP10.
What is the alternative?
It has been suggested that I create an ISO disc (USB dongle) from disc 1 of XP11. The advice given indicates that it will work. Having found several software packages to make the conversion I have not ventured into the conversion. I am currently seeking further info about one package. the link can be found at https://www.lifewire.com/how-to-burn-an-iso-file-to-a-usb-drive-2619270
I will advise on the outcome through a private message.