Sorry man, but I do not understand...
As you noticed, the custom button is inside the Edit form (EditFormType="WebUserControl") of the grid.
So, the code of this button is in the ascx.vb file.
What GridCommand I would use for the FireCommand?
In other words, in the Item command, what would be the e.CustomName?
Forgive me if I don't understand, but maybe you should take a little more time reading my scenario above.
I will tell you something a little more general.
Most of the time, you (the support people) throw us a link of the Telerik knowledge base which explains the relative topic, but the actual problem is rarely addressed!
Sorry, but this maybe save you time, but it does not serves the purpose...