Try using this sail repair tapehttp://www.admiralpsp.co.uk/psp/product ... tapes.html
The kite repair tape that they offer is exactly the same as the spinnaker repair tape. I had a LF Havoc that had a 1m + tear on the first week I got it. I used this tape and it held out for 3 seasons until I retired the kite. I did not sew over it.
The tape is extremely thin and the glue is very strong. I highly recommend it.