Hm, I can't see the website because it is password protected.
Yes yes, well I think you can probably make a modal open itself when you click on something. But it won't easily be possible to show the gridder content inside of it :/. You can extend lay theme a bit with your own functionality but just up to a certain point. I'm not sure if I know what you mean by "WP Pages".
If you are comfortable with programming a bit and you want to use the gridder, I think it is probably easier to use laygridder.com
If having modals like that is really important to you and a dealbreaker, then maybe you don't want to use lay theme anymore. Then you can get a refund if you want.