So there you have it. When it comes to the size of your massive feet (or hands), the only thing you can really be proud of is... the size of your massive feet (or hands).
How can I get my girlfriend to masturbate in front of me?
I'm not exactly sure this is the correct attitude, so let's start there. You shouldn't have to "get" your partner to do anything. There should be no smoke-and-mirrors, sleight-of-hand trickery involved when it comes to fulfilling sexual fantasies and desires. The only way to truly "get" what you want from another person, especially in bed, is to ask.
There is nothing wrong with self-lovin’. In fact, it’s something we should all do on a regular (daily?) basis. And doing it in front of someone else is more than hot -- it's empowering for both people. However, your girlfriend might not want to do this for a variety of reasons: 1) she's shy; 2) it's personal; or 3) a hearty combo of both. Masturbating IS personal, and that's why it's so wonderful. We don’t have to worry about pleasing anyone but ourselves. Maybe we are shy about the faces or noises we might make while we are on display. Sex faces and sex noises when it's part of a duo are easier to ignore because you're both in it together. But when it suddenly becomes a solo act, stage fright might ensue. So if this is a discussion you want to have, you can start by complimenting her while you're having sex in person. Tell her how sexy she is when she gets off. This will help her feel confident and attractive. From there you can work up to exchanging sexy pics, if you don’t already do so. As she feels more comfortable putting herself "on display" for you, you can work up to private viewings. But be prepared to do the same for her. You know, tit for tat. Quite literally.