5-day L Visa extension

I have a 2 year multiple entry L visa valif for 30 days stay per entry. I would like to stay for 35 days on my next trip. Does any one know if I can get the 35 day stay from the Immigration desk upon entry at Beijing airport if i can show them my airline ticket booking to prove my planned departure date? This would same me the effort of having to separately applying for the extension at a Public Security Bureau.