I don't know of any way to let the scrub speed be rendered. Your best bet would be to render the project at normal speed, import the resulting rendered wav to a new project, and stretch it (and change your properties to force the length and pitch to change accordingly). Assuming you're working with multiple tracks and/or multiple sounds on each track, it would be a very difficult task to do any other way.
You can also just take the resulting rendered wav into Sound Forge and pitch shift it.

Pumice