Hi! I think it is possible: the extension could temporarily turn "Send all input to VKB" off when it is opened, then restore it after the window closes. I might look into this at some point, but this is a low priority project right now
Until then the best I can think of is to set up a keyboard shortcut that is never used by the VKB (one of the F-keys for example) to easily toggle the "Send all input to VKB" action.