jqGrid Custom Edit Dialog

I am working to an application that uses jqGrid. The problem is that the edit dialog that should appear at row edit must have a specific layout. So I would prefer to load it via ajax and then send the data back to jqGrid manually. I searched a lot on the forums but I could not find an example of how to do it.

So, I just need jqGrid to fill the edit dialog pop-up with custom content from a PHP script.

UPDATE: THe idea is that I have a form generator, where the user sets the position/width/heigh/visibility of the edit fields... and this must be used in the edit dialog.