Connect Front USB to Mobo

Hello,
This may seem like a trivial question, but it's really annoying! I've been putting togther a new PC from some spare components, including a fairly recent gigabyte GA-EP43-S3L mobo and a case from an 8-year old Evesham PC. All works fine, except I can't connect the 2 front panel USB ports to the mobo. The cable which came with the case has a connector with two rows of 5 holes, which should accept the appropriate nine pins - except it is too chunky! The USB headers on the mobo are surrounded by little plastic enclosures which will only accept a slimmer connector - though the nine pins seem to be in the same places. I've enquired at various stores (maplins, yoyotech in London)and you simply can't get this type of internal USB cable. The stock answer is "they come with the case". Well mine don't fit! any ideas ?