I find making a frog do anything is a particular nightmare, however my best guess( I don't have any real data) on how is....
Find something a frog wouldn't be interested in, some white emulsion perhaps. then put it behind the frog. Hopefully the frog will then blank it.
Substitute gradually more interesting things in place of the paint over a period of weeks, hopefully the frog will blank those too.
Finally put IT behind the frog(whatever it is) and that should make the frog blank it.
btk