I have seen in the past UKs with matching sporrans that clipped onto the front belt loops- but a quick check at the website turned up empty...

if you need the extra storage i say go for it but you get used to (and actually enjoy) those breezy days and it becomes a reflex to hold the front down to protect your modesty.

if you kilt flying up is that much of an issue,you can stitch a small pocket at the bottom in the center on the underside of the under apron and put in a few nickels (or fishing weights if you have any available in your area). be sure to wrap the nickels (or weights) in fabric first to prevent them clinking together and lightly stitch the pocket shut. the weight will hold the front down a bit more without being too noticeable. You can undo the stitching closing the pocket when you launder the kilt (or leave them in as the nickels shouldnt tarnish (DONT USE PENNIES FOR THIS REASON) but they will clank if you put the kilt in the dryer and cause extra wear in that area if you tumble dry the kilt.
this will also help your apron to fall more quickly when you sit down with your knees apart.