Well if I understood well, off course there is a way.
First: open your form with the form manager, click on the icon for the main form (not a page or a section) and open the advanced options tab (the one next to properties tab).
Second:Once you're there you will see an option that says "use alert on errors", just check that. This will make use of the browser popup alerts instead of the joomla system warnings.
I don't know if that was what you were looking for, I hope it will help. Let us know here and maybe we I can give you some more help.
Greetings!
TeNsHi SaMa