What you may have to do is... Get sum stem spacers and put them under the stem so the stem sits a few mm above the steerer tube then fit a start nut and top cap (see below link)http://www.ebay.com/itm/BBB-BAP-02-1-1-8-Silver-Aluminum-Headset-Top-Cap-Star-Nut-25g-Complete-/300675440729?pt=LH_DefaultDomain_0&hash=item4601a72059Thats the only way i can see around it thats cheap and easy... Sorry i can't help you moreLet me know what you think?
So the top of your forks are threaded on the outside??