& a quick Google later...
I found the following links...
What is a CF 4455 & why do I need it ?
Here's a Cool Online version that you can fill out ( Online ) & print
More help on what to do with the CF 4455
This last link seems to suggest that you need to get the form certified at you local Customs office ... so you need to go there.
I would :-
Take the watch, & a magnifying glass / Loupe ( make sure you can remove the watch back with your fingers ). Describe the watch in the Item description as ( Example ) Omega flightmaster Movement serial number 31,111,222.
You can remove the back & show the customs official to prove it IS the watch you claim it is. Hopefully that should be enough, he'll then certify the certificate.
& you can send the watch on its way. ( you need to send a copy of the CF 4455 with the watch, Omega should know hwat this is & how to fill it out. They'll send it / a copy back )
When the watch comes back, Omega will use the movement serial number on the invoice. I WOULD NOT let anyone open the watch now ... but since the Invoice identifies the watch with the same number as the CF 4455, there shouldn't be a problem.
Finally Philip, in the 1st link, there is a link to "find your local customs office", use that, then call 'em.
I hope this helps.
S.