The Pischei Teshuva 142:1 discusses whether the sofer who writes the gett can be the shliach to deliver the gett. The problem is that he has to say upon the delivery "b'fanai nichtav ub'fanai nechtam", which implies that it was written by someone else in his presence, and is inaccurate since he himself wrote it. The other option is to say "Ani kasavtiv ub'fanai nechtam", but the problem with that is that it is a shinuy from the takanas chachamim.
There seems to be a clear proof from the gemara today that if one actually wrote the gett them self, they cannot use the language of "b'fanei nichtav". This is evident from Rav Ashi who does not allow one of eidim who signed the gett to be a shliach to deliver the gett since he will have to say on his own signature "ani chatamti" and on the other "b'fanai nechtam", and will not be completely using the method of kiyum, nor will it completely use the takanas chachamim. Why not let the shliach just say "b'fanai nechtam" on both signatures (even though one of them is his own)? Clearly we see that if it is his own signature it would be sheker to say "b'fanai nechtam". Similarly, if it is his own writing it would be sheker to say "b'fanai nichtav". This is a big question on the Radvaz that is quoted in the pischei teshuva who rules that although if he said "ani kasavtiv" it would work (and is not considered a shinuy from takanas chachamim), ideally he should say "b'fanai nichtav". The Radvaz argues that it is not michzi k'shikra since it is true that it was written in front of him. If the Radvaz is correct, why would Rav Ashi not offer the same solution?
Practically speaking, I have had that situation (and R' Nota Greenblatt who is often the sofer and shliach has the situation all the time), and R' Nota holds that one should say "b'fanai nichtav, ub'fanai nechtam, Ani kasavtiv, ub'fanain nechtam".