I'm pretty sure you can with KISSMetrics. They have a PHP/Ruby API where you can set the dates for stuff. Just run all your old event data through the api setting the dates when they actually happened.
You can, but we'd really like to talk with you to understand more about what you're trying to do (if it's a valid use case for you, it probably is for others, and we want to make sure we get it).
Email calvarez at kissmetrics.com and I can help you get started.
