Can I share my MacBook Air's wifi-connected internet with my iPhone?

Ok, Ill keep this short and sweet...

I travel to Puerto Vallarta frequently. The hotel I stay at has WiFi internet only, however the signal is weak inside the rooms. I purchased an extrenal antenna/booster (connected via USB) per several Apple fan suggestions.

So, while my MBA may connect just fine with the booster, my iPhone 4S cannot connect to the weak hotel WiFi when inside my room. I want to share my MBA's internet to my iphone..........

... is there any possible way of doing this without paying for tethering? I have been scouring the net for two hours - and cant seem to figure it out... Id guess you would call this reverse tethering?

Thaks in advance for your help!

Jeff