Hi Polly,
I'm glad you found the setting to default the Actual Dates to their Planned Dates (for those interested, see Setup > Project Preferences > Tasks & Issues > Actual Dates, and choose either Now or Planned on both options).
If that setting is too broad (since it is global), another option would be to leverage our "http://store.atappstore.com/product/uberfilter/">UberCalc solution, which could automatically set these Out Of Office Tasks' Actual Start and Completion Dates to their Planned values once the Planned Completion Date is in the passed (and MUCH more).
If you're interested in more details, please drop me a line at doug.denhoed@atappstore.com.
Regards,
Doug