You could do it with events. you will have to get rid of the graphic after it dies then have the event switch to a diffrent page where the event move route is random then after a while have it switch back to the first page where it shows the event and you can battle it.
I dont have RPG Maker in fromt of me at the moment so if you need more help just ask and i could make a demo or something (if you have RMXP)