Someone

portal:starttouch(ent)
    nocollide = make nocollide between world entity & object
	ent_twin  = make twin entity on other side of portal
    nocollide_twin = make nocollide between world entity & object twin
end

portal:touch(ent)
	
	// do stuff to keep the two physics objects in sync
	
end

portal:endtouch(ent)

	remove entity
	remove nocollide
	remove twin_nocollide
	
end