Get a non-locking cap is the easiest way.
Bought mine for £50 from
http://www.moto2.co.uk/ but I think that was a show special.
Saw these on ebay today which might be worth a look...
http://cgi.ebay.co.uk/ws/eBayISAPI.d...tem=7965632353 Note that the round caps are universal - same for 916/748 as for SS, etc.
More at their shop -
http://stores.ebay.co.uk/The-Excellence-Parts-Shop