You could implement an Auto-buy system where you can buy "RG Coins" in 10, 100, 1000 and then use that to purchase the account/money.
BUT, people can still scam, heres how:
User A buys 1000 RG coins for $100. The system/The Elite adds the coins to Player A's account. Player A then buys 1000 RG coins worth of RS Gold from Player B, then receives his RS Gold. Player A then charges back.
Then alot would be on The Elites shoulders because he was "in control" of what is now Player B's money.
Also, with a system like this, there would most probably be a lot of vulnerabilities in how the money is added, traded and sold throughout the forum. And one hiccup with the "Virtual Currency", and all hell would break loose.
You can't get any safer than a Middleman in my opinion.