Man a filter for XnView what would do something like this would be awesome... It could be done.
XnView Tweak UI - Tool to customize your XnView beyond the regular XnView options. UI-less Settings - Documentation of all the hidden settings in XnView. XFAM - Tool to create and customize XnView file associations.
tiltshiftmaker.com (Free online service) Use TiltShiftMaker to easily transform your standard photos into fun tilt-shift style miniature pictures.
Stefan Hafeneger: TiltShift (Freeware, Mac-only) TiltShift is an Aperture Edit Plug-In for computer generated tilt-shift photography. The software allows you to create fake miniature versions of regular photos, simulating the effect of expensive tilt-shift lenses.
onOne: FocalPoint (Commercial Photoshop plug-in) Add realistic depth of field to your photos.
I'll keep looking for a plug-in that works with XnView. No luck so far
Art&Mobile: TiltShift Generator (Freeware, AIR-based) TiltShift Generator is a web service that adds cool camera effect to your picture on the fly.
This app is originally made to improve my cheap iPhone Camera's potential.
dev.LUX: Tilt-Shift-Focus (Commercial, Mac-only) Create Tilt-Shift effects on your mac with a few clicks. Turn your photos into miniature worlds.