This might work.....

First get the "gconf-editor" from here:

http://maemo.org/downloads/product/gconf-editor/

then click on "system", then "osso", then "af".

There is a check box to indicate if the USB cable is connected to a PC. You might need to clear the check box.

If you don't want to download the gconf-editor, you can
edit the XML file directly.

/var/lib/gconf/system/osso/af/%gconf.xml

you will find a bunch of settings, like if the camera is out,
if the mmc cover is open, if mmc is attached via usb, etc.