RE: Letter Cake

If the cake is left completely naked, like the picture, the only thing I know that would help with drying out is to paint all surfaces with a simple syrup. If it is acceptable to your customer, applying a thin covering of buttercream, in the semi-naked technique, would help lock in the moisture.

You definitely need to wait until the last minute to add the flowers, unless you have picks that hold water to keep them fresh.