One method that worked for me is to use a finger or thumb (well-trimmed fingernail!) and very slowly, patiently, massage and edge the foot off the glass a millimeter at a time. They let go eventually; you can feel as you go to make sure nothing is getting damaged. This does involve your bare hand in the tank, so not necessarily the best option.
Another thought: anemones move wherever they're comfortable; if possible, it's best to plan your tank around that aspect of their behavior.