Try putting out trails of ferretone leading to the house from all
directions, and put an open cage in the yard with food/water/blankets and
check it often.  Or borrow a humane Have A Heart cat trap which will not
hurt the ferret and put some food/water in to entice him, and check it
often.  Don't leave it in the sun or rain though or he will get too
hot/heatstroke, or wet.  Good luck.
[Posted in FML issue 3390]