OK that problem's solved then. Making starbases uncaptureable was easy.
You'll need to go into CIV4PromotionInfos.xml and set the capture percent for any promotions that will have it. I'm pretty sure the order of xml fields in the file is important so place <iCombatCapturePercent> after the <Button> line. Also in CIV4PromotionInfos.xml you only need to put a line in if the promotion has that ability so you don't need to add <iCombatCapturePercent>0</iCombatCapturePercent> to everything else. Keep in mind that each promotion is calculated separately, not added together. So if you had five promotions with 20% chance of capture, it's not 100%. It's actually about 67%. With the CIV4PromotionInfos.xml file I used I only had capturing on neutron blaster, and bulrathi, at 50% and trained officers at 100% for testing purposes, so make sure you change those. The changed files are attached, hopefully I didn't forget any.