Dunno about Malta, but I've seen people trying to do similar in the UK, when they've been unable to sell their house by more conventional means. Many of them ran aground because of legal red tape, but with perseverance it can be done in the UK. Maybe in Malta too?
In the UK, I think you have to get an independent promoter/overseer to ensure no foul play (such as your friend or relative "winning" the prize). Another requirement appeared to be that some skill is involved in the competition - ie answer a question - rather than total chance, such as a lottery.
It's probably best to ask your lawyer for legal advice on this.
Some countries are quite freaky about gambling. It'll be interesting to hear how you get on. Please let us know. 8)