what you want to do is start looking for private buyers. i have gotten a couple buyers from guildmates and one from trade chat.
I start by asking in trade channel "trading gold for gametime pst, need ~6months" and if anyone gives a serious response, ask if they are willing to take the convo outside of game (i often use a vent server as a chatroom). if they ask why tell them its just a precaution to keep it off record, but really its a test of their true interest in making a deal. once out of game you ask if they would be interested in direct gold to cash via paypal/moneybookers or whatever you use. if they turn this down or if they decline to take it out of game, you can still try and make a trade for game time via blizzard store.
the key is to act confident in what you are doing, dont seem unsure or afraid. I always offer and oblige to let them know my main character as an act of trust against scamming, they know who I am and that i wouldnt ruin my realm reputation over a scam. if they claim to have reported you dont freak out, they have no basis for a report until you actually trade, at which point they are just as reportable for buying.
my realm regularly has gold spam bots advertising 1-2$ per 1k, i however trade at 3$ per 1k and tell customers that the price increase is a hell of a lot better than a ban after trading a gold spammer. this comes out to 5k for a 1month code from bliz store, 10k for a two month scratch off card.