I was unaware that Thorn advised against kickstands until a couple years after I installed a Greenfield one.
It is my understanding that Thorn may refuse to honor a warranty if you use one like mine, so think about this carefully.
Mine, if the front wheel can roll, the bike might roll forward and fold up the kickstand. So, sometimes I have to lock the front wheel with an elastic on the brake lever. Third photo (photo is a different bike, but same method).