hi andrew
that's a cool workaround for custom searches in the AGOL apps until something better comes out, thanks.
we're already experimenting with some lightweight services for AGOL Org accounts using Arc2Earth, so I decided to build your workaround into a full service without the need for an ArcGIS Server. You point the service back at any Feature Service you have hosted in your AGOL account, set a few options and voila, simple search on multiple feature services.