A bit late for this specific post perhaps, but I just came across this in the CBP FAQ which might be of future use for people in a similar situation.

Basically it states that if you left the USA, and then find the I-94W stubs still in your passport, as long as you departed via commercial air or sea carrier, there is no need to do anything.

https://help.cbp.gov/cgi-bin/customs.cfg/php/enduser/std_adp.php?p_faqid=752&p_created=1077641280&p_sid =JIdmApQj&p_accessibility=0&p_redirect=&p_srch=1&p _lva=&p_sp=cF9zcmNoPTEmcF9zb3J0X2J5PSZwX2dyaWRzb3J 0PSZwX3Jvd19jbnQ9NzEsNzEmcF9wcm9kcz0mcF9jYXRzPSZwX 3B2PSZwX2N2PSZwX3BhZ2U9MSZwX3NlYXJjaF90ZXh0PWRlcGF ydHVyZSBjYW5hZGE!&p_li=&p_topview=1