Sorry, but about the only thing you can do is to turn off the playback controls. They are either visible or not. No way I'm aware of to disable action or whatever. Maybe if you know Flash pretty well and exported the project to Flash you could do it.
I once tested to see if I could influence the tab order of objects and it seemed the order went from left to right and top to bottom. So another possibility would be to add an element to the slide. Perhaps a Click Box and place it to the right of whatever object you are asking them to press Tab on. My thought here is that perhaps the focus would then shift to the next object and prevent them from placing focus on the playback controls. You could configure the Click Box with no action when clicked. Its only purpose would be to allow focus to be placed on it instead of the playback controls.
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Rick, thank you for your reply and for your thoughtful comments. I was hopeful that there would be a way to turn off the shortcut keys during playback, but if my only option is to turn off the playback controls, then that's what I'll do. Thanks again for your reply!
Only want to add a comment because you mentionend to include the playbar for possible navigation by the user. If you are using CP4 (do not remember you mentioning the version), you can add the TOC to enable navigation by the user. And keep the navigation possibility active. Just a tip,