I dont own a fiesta but ive seen a number of times on here, aparently its common on the fiesta for the oil return pipe off the turbo to choke up when the oil is cold and thick (ive also seen how long, bendy, and thin a FRST oil return pipe is so i can believe it) I believe there is a big oil return conversion which is meant to sort the problem.

Its worth checking its not just blocked aswell....aparently this is also common.

Basically the oil all builds up in the return pipe and cant drain away quick enough so it gets forced out of the seals causing the smoke, but obviously once warmed up the oil is thinner and drains away quicker. IMO you would be better to try this, and if its not this its still a worthwhile mod.