Use her mouth...

I lean over and cuff her hands behind her back, then point to my crotch. "Take out my cock, using only your mouth."
Helen smiles and fumbles around with her lips and tongue until she finds my zipper, then she tugs it open. After that she reaches in and pulls down my boxers and voila, my hard cock springs out. "Wow, its soo big." Helen says, blushing and biting her lower lip sexily.

I stroke her head and my cock. "Yes, and guess who´s gonna suck it." Helen looks at you with a look that says `Do you really expect me to answer that´ but she obliges. "Me, Sir?"
"Yes, now make it good." I say, leaning back and leaving her to do all the work. She eagerly does so after licking around the head for a while and then taking half of it down in one go. She start slobbering a bit over it and runs her tongue along the underside of my cock while she sucks it. She tries to take it down her throat but gags and pulls back, yet my cock never leaves her mouth, and she maintains near constant suction.

After about fifteen minutes I feel a familiar surge in my groin. I pull at Helen's hair to get her attention and she stop sucking. I then ask simply. "Where do you want it?" Helen first looks at me as if she doesn´t understand, but my twitching cock answers the question for you. She answers quickly...