Unfortunately there's no easy way to accomplish that. You can try going into List view and copying the appointments. In List view you can copy as many appointments as you want. The catch is you either have to already have an appointment on the date you're copying to, or you need to copy one of the appointments in Calendar view first so that the day will show up as an option in List view.

Once you have an appointment on the target day, switch to List view by clicking on the View toolbar, selecting Change View, and selecting List.

Then click on View Settings. Click Group By, and select "Start". This will sort the list by the start date. Find the appointments you want to copy, and hold down Ctrl while clicking them to select the ones you want. Then hold down Ctrl while dragging them to copy, and drag them to the new desired date.

It's a little awkward, but it should accomplish what you're trying to do.

Hope this helps.

-SW