jQuery Grid Plugin - jqGrid

I am looking for some help/advice with a custom element in my edit dialog (editGridRow). One of the input values is chosen from a list. However, there are too many items to load into a drop-down list. What I would like is a custom (textbox & button) control that does the following:

1. enter some text in the box
2. "click" the "find" button
3. the text is passed to the server & the server performs a search
4. the resulting "select" list is returned to the control
5. the user selects from the returned list

I don't understand how to communicate with teh server in mid-form (steps 3 & 4). Any suggestions and/or examples would be greatly appreciated.