To actually answer your question, thickrod, here are a two practical ideas:
See if she is comfortable talking about past relationships or sexual encounters. If she isn't, you may be out of luck putting a lot of stake in what she's going to think about your size. If you are trying to interest a girl who loves size, she's going to enjoy talking about sex and similar topics. SO, if she IS interested, ask her about her past relationships and flames, and tastefully share some of your own stories. I guarantee you there will be a discreet way to hint at your size, especially if you've had girls react to it in the past. Example, "Well, let's just say some girls have been surprised at some things about me..."
Ask her what kind of guys she goes for (which is a typical topic in flirting), and nonchalantly ask if she has any preferences, physically. She'll probably say, "What do you mean?" Then casually rattle off a list of things- "You know, eye color, height, build, size, you know..." She'll probably catch that last one and laugh at it. If she takes the bait, you know she's probably catching your hint and will want to talk about it. If she ignores it, you're probably barking up the wrong tree.
Good luck, stud. Hope you find a girl who enjoys size as much as we do.
-Aly