Changing selection behaviour on a ListView.

Question

I'm building an application destined for a touchscreen system. This application uses a ListView control that I would like to support multi-select with. However, since this is a touchscreen, the user can't hold down Ctrl / Shift to multi-select items so I've given them some toggle buttons to flag this behaviour.

Has anyone successfully overridden the item selection events in a listview to behave like the "ctrl+Click" behaviour without the Ctrl key actually pressed? This has to be able to select multiple, and de-select items.

I've had less than stellar success defining my own extension to ListView to try and change this behaviour with MouseDown/Up events, and I haven't had much luck on Google either. Surely someone out there has done multi-select on a touchscreen/PDA, I'd like to have a chat if you have. ;)