Grid editing + CustomField: focus handling?


I’m trying to make an editable Grid (unbuffered mode) work with a CustomField (layout with textfield + button).
The field works reasonably well, but the problem is that when the user presses Enter to navigate to the same field on the next row, the field on the (new) editor row does not receive focus. This basically defeats the whole concept of fast unbuffered editing using the keyboard.

How exactly should I proceed to make my field handle focus? When focused, the CustomField should pass the focus to the contained TextField. It seems that the Grid widget is looking for Focusable widgets. Have no experience in client components, esxtensions, GWT and similar client-side stuff. The less intrusive the solution, the better. Do you have any suggestions please?