I think when your three year old child wakes up in the morning, you need to get up with him. I think allowing him to play by himself while you catch some extra zzz's is probably not such a great thing.
Granted, I do not get up a half hour before my children to have breakfast on the table (my mom did) but when they are up, I immediately get up...even if it's at six. Sometimes it's at five-thirty. Sometimes I only get four hours of sleep. Sometimes I try to go to bed earlier.
The problem with trying to punish this behavior is that you created this behavior, not him. He's still a toddler, and you are leaving him on his own when he wakes up. He wants YOU when he wakes up, so he is yelling to you in hopes that you will come "get" him. I have a feeling that if you went in to him right away when he wakes up, he wouldn't be yelling. I definitely don't think he's doing anything wrong...for one, he may understand he's yelling, but do you really think he understands why you don't want him to? No. He doesn't know what having a baby is going to be like.
If you really wanted to extend his morning wake up time to seven, try keeping him up a little later, or systematic awakening (where you set the alarm for before he wakes up, and then as he gets used to waking by an alarm gradually set it forward a bit at a time.)
I'm not trying to be harsh...how I would love an extra 20 minutes (hah, an extra two hours) every morning...but I don't get it. :( Really, I think your only solution is to go to bed a little earlier and get up when you child gets up.
I also can't believe someone suggested if "he wakes you up you should make him stay in bed." I mean, do you REALLY want to turn his bed into a punishment zone? Hah, good luck with that...he'll never want to sleep! Um...we're supposed to be awake with our children. If they wake up at six ready to go, then that's what time they wake up.