In my experiance a decent 125cc bike will give a porche Boxter a run for its money everytime..

So...With your wheight in the middle of the bike..possibly leant forward slightly
Whilst at a standstill Select first,
Get the Rev's to that point when it begings to make its best power. (dunno wot the CG's are like for Revs but experiment..Don't red-line it though!)
Left foot surpporting the bike, right foot covering the rear brake,
let the clutch out quickly but smoothly ,
Let the revs get up, and change into 2nd later than you would for everyday riding,
then wind the throttle on and go up through the gears as normal. By the time your in 3rd mr boy racer should be long gone.

Find a quiet industrial estate or similar and practice , practice , practice.
If the front wheel lifts and the bike starts to wheelie(unlikely, so dont worrie to much

) ,simply back off the throttle, If it gets silly high..Jump on the REAR brake and keep your wheight central.
If it wheelspins (more likely) just back off the throttle until it stops and reapply it , or back off and change up a gear.
Hope that helps. Ride safe and make sure your rear tyre is'nt on a white line when ya pull away