Doing Planning Poker Remotely?

Has anyone out there worked out a clean way to do Planning Poker remotely? We have development teams with people in multiple locations, so we conduct our planning sessions via conference call and screen sharing.

If you're not that familiar with Planning Poker, it's a quick way to size stories without getting down to the level of person-days. Story point sizings are based on your past experience - an 8-point story should take rougly as much design/dev/test/doc effort as an 8-point story you've finished in the past. You talk for a few minutes about a story, and then everyone in the planning session does a "secret ballot" where they choose a story point sizing. Then you discuss the largest and smallest sizings, and come to a consensus on what the sizing should be. You can use the story point sizings to plan how much work you can do in an entire release, across several sprints.

There's a Planning Poker plug-in for Sametime. The plug-in was OK - you could set up a planning session with a group of people, and enter the stories to be sized. Then when you selected a story, each person could submit their estimate, and it wouldn't show the estimates until everyone had submitted. But it's often a problem for people to get the plug-in installed and working. For example, if people had the wrong version of Sametime, or if they were using a Mac, it wouldn't work for them.

Another thing we have done is a standard group chat where everyone just types in their estimates, and everyone can see them right away. There are a couple of problems with that - for one thing, some people (mostly newbies) will refuse to submit their estimates until other people (usually the team lead / scrum master) submits theirs. Also, once a few people submit their estimates, all of the other estimates seem to magically become the same number. Which means that people are changing their answers based on what they already see on the screen. Sigh.

A third thing I've seen scrum masters do is set up a second display where they have an individual chat session with each person, and no one can see the sizing estimates except for the scrum master. That works resonably well, but it's still kludgy.

Can anyone recommend a better way to do this? What do you do?