At my company, the project manager is usually working on 2-3 projects at a time. I'd like to be able to track this on the individual project plans.

I'm thinking I could create a single task "Manage Project" and assign the PM to this at 30% (or whatever). Is there a better way?

How would I make this task run the entire duration of the project, even as the duration may change? For example, if the project is late by 2 weeks, this adds 2 weeks of the developer, plus 2 weeks x 30% of the PM, something like that.

Thanks for your suggestions.