Two ideas come to mind:

Perhaps you a sheet of heavy plastic fitted to the top of the candle, so that it holds the design in place during shipment – the plastic sheet removed by the recipient upon receipt.

Another solution may be to find a double glassware set for your design – where the base glassware holds the design snug in place, and the top glassware holds a separately wrapped (gel) votive candle that can be unwrapped by the recipient.