You could do so by volunteering your skills, possessions and/or time at www.fortheloveofwispa.com to help create the advert itself.
I can now show you the resulting advert:
Cadbury's - For The Love Of Wispa Advert
It is all so simple and grand. I really like this advert in the entirity. However, at 2 minutes 11 seconds in length, I am sure it will not get much TV air time in this form.
As with the "drumming gorilla" ad and the "racing colourful vehicles at an airport" ad, it seems like Cadbury's are sticking to commercials that are just purely associating themselves with having fun. I think that is a smart way to go in our health-conscience society and I hope that Cadbury's continue with this route.