The cic website states that people who are common-law partners of certain foreign students who are studying full-time.
Me and my girlfriend are common law and she is currently enrolled in a post secondary institution and has a study permit up to September 2014
Is it possible to first extend my work permit without LMO and after Septmenber with LMO (without the recruiting efforts of course).
You want to obtain an open work permit based on your wife's study permit. Others who are in similar situations are posting in the International Students section of the forum and you'll find threads there on the subject of OWP (open work permits) or SOWP (spousal open work permits) for spouses/common law partners of international students. This is why I've suggested you post there.
You cannot extend your current work permit without an LMO. You need to apply for the open work permit if you don't want to go through the LMO process.