out-of-office notification message, plugin?

I used to have a method of showing a message on our shopping cart and we would use it to let customers know if we were out of office for a while (and thus their orders would be delayed). I'm curious if there is an "official" way to set notices like this and/or if a plugin would be the best route?

A widget plugin would be best.  You may be able to use the free 'All in one' widget plugin.  I think you can target one of these widget zones
OrderSummaryContentBefore
OrderSummaryCartFooter