Is there a way to tell netsuite to use this split-pane multi-select instead of the standard one? this is the dashboard tiles form — see how the role allows you to choose from the left side and see all your selections on the right?

This is determined by a) the number of options in the drop-down and b) what you have as the number in your Preferences under Preferences->General-> MAXIMUM ENTRIES IN DROPDOWNS. If the former exceeds the latter, NetSuite renders it as a popup search instead of a regular drop-down.