So, I got my shiny new bike recently. Then, my wife started talking about getting a used BMW car. Long story short, I caved and she got her BMW. The car ran great until she accidentally put in regular unleaded instead of premium. Shortly thereafter she got a cylinder misfire engine code. After checking around on BMW car forums, it seems BMWs can be quite sensitive to low octane gas and it isn't uncommon to get a check engine light if premium isn't used. Her tank is 3/4 full right now.

Now my question. Would the best way to raise the octane be to put in 1/4 tank of 110 octane racing gas, or to us an octane booster? If an octane booster is the way to go, what brand?

Thanks!!