a: put on a pair of overalls buy a rear slick sling it over your shoulder run up to the gate and in your best pigeon italian shout "tyre! tyre! for Ducati let me through very urgent"
or
b: put on a pair of orange overalls get yourself a red flag run up to the gate and shout "quick i have to flag this practise i'm late"
I got in years ago, on a marked up courier bike delivering an 'empty' jiffy bag with with parts for HRC
The jiffy bag did come covered in Honda stickers etc as it had originally had some HRC bits in once. Took a lot of blagging and a mate on the inside who had warned the gateman that a courier was turning up with some urgent bits