Give your toys male names as mentioned above, then increase the amount of dirty talk during foreplay. If she seems to like it, ask her in a non-judgemental way and allow her to set the boundaries first. Then start asking her ~During sex~ whisper in her ear.. . "You want a another cock don't you?. I want to watch you" and do that several times to gauge her reaction. Do it softly and clearly. IF it turns her on.... ask her if she wants to set some rules where you two can do it in the future..... It worked for me. We have a regular once a month (or less) threesome with a buddy of mine. He and I take turns on her, then I watch them. Really hot.