Not with Access' Zoom Box, but you can easily "roll your own."
Place a large text box (call it MyZoomBox) on your form, sizing it to your
liking. Assign the same Control Source to it as the field you want to expand,
and make it visible by double clicking the field you want expanded.
Substitute the actual name of your field to be expanded for YourTextBox.
Private Sub Form_Load()
'Make the textbox invisible on loading the form
MyZoomBox.Visible = False
End Sub
Private Sub YourTextBox_DblClick(Cancel As Integer)
'When you double click the field, make the MyZoomBox
'visible and move the cursor to the beginning to
'deselect the text
MyZoomBox.Visible = True
MyZoomBox.SetFocus
MyZoomBox.SelStart = 0
End Sub
Private Sub MyZoomBox_DblClick(Cancel As Integer)
'Double click the MyZoomBox to close it and
'return to your original field
Me.YourTextBox.SetFocus
MyZoomBox.Visible = False
End Sub