Let me see if I understand correctly: you want your bets placed by someone else, but you decide which bets are placed and you provide the funds? I suppose this would be for sports right? I do know a service where agents place your bets you ask for, this service is provided by AsianConnect and BetInAsia if I remember correctly (in certain bookies, no exchanges), this works if you are on the venue watching an event and you want to place live bets with certain edge over the market (if I remember correctly this is done through skype), this is still risky as the bet can be rejected by the bookies for whatever reason they want and this is non-negotiable (I have seen cases where this happens).
If you mean you want a particular person (not a betting agent) to place your bets with your money on any casino or bookers that doesn't allow third parties involved, then I have to tell you this is a terrible idea that will lead you to guaranteed losses, betting on someone's behalf is prohibited by all casinos without exception and the few bookmakers that permit this only allows this if it's done by an authorized agent.
You don't need anyone to be involved in your betting, simply register in exchanges, bookers or casinos that allow your jurisdiction, it really is that simple, and if gambling is illegal in your jurisdiction then there is not much to do, you can still contact betting brokers to see if they can offer you their services (the two I mentioned earlier)
Automatic translation: