In sefer Atzei Besamim # 34 (from the rosh kollel in milwaukee - R' sederovic) he discusses a very interesting question. A man was being me'agen his wife for many years by refusing to give a gett. They managed to convince him to give her a gett over a shabbos that he was in town, but by the time shabbos would be over he would be gone. Is it permitted to set up the sofer, eidim and shliach on shabbos, to write sign and deliver the gett after shabbos, or is the set up also assur?
The first question is would one be able to give a gett on shabbos in this circumstance. The gemara permits someone who is dying to be makneh the gett to his wife with a kinyan chatzar (or agav - see rashi), but not to move the gett. The Rosh explains that it is possible that if need be chazal would be matir the issur to move the gett (muktzah) also, just that they prefer to be matir the issur of making an acquisition on the chatzer [The Rosh explains that we already find that they were matir kinyan for a sh'chiv meirah in baba basra 156b, so they would rather be matir something that they were already matir elsewhere. The Ran explains that it is less recognizable that she is doing a kinyan than it would be to move the gett, so they prefer to be matir the issur kinyan. The korban nesanel (3) suggests that they prefer to be matir an issur that will be simultaneous with the gett going into effect]. However, aside from the issur kinyan on the chatzer and the moving of the gett, there is also an issur to divorce on shabbos. Tosafos and Rosh say that they were also matir this issur for a sh'chiv mei'rah. Why? Tosafos here says that it is to prevent her from falling to the yaveim. But, in Baba Basra the gemara says that it is to prevent the sh'chiv meira from tiruf da'as and causing his death [that is why they were matir kinyan on shabbos. The Rosh here and Tosafos there both connect the heter in our sugya to that sugya]. The sefer atzei b'samim makes a very good point. If the heter is based on igun, it should apply in our case as well. But if the heter is based on tiruf da'as of the sh'chiv mei'ra, that is not applicable here.
But it seems to me that the entire issur geirushin is not applicable in this case. The sefer Atzei Besamim suggests that whether the issur geirushin on shabbos would include setting up the sofer/eidim/shliach depends on somewhat of a discrepancy in Beitzah 36b between the simple reading of the gemara and tosafos whether the problem of divorcing on shabbos is because of leading to writing or making a kinyan. He suggests that kinyan would not apply to setting up the sofer, eidim and shliach, but he assumes that the issur of coming to write would apply. It seems to me that even if chazal were normally concerned by kiddushin, gittin and other business transactions that you will come to write, they were only gozer on the ma'aseh of kiddushin/gittin.... but not on the preliminary set up. The setting up of the sofer/eidim/shliach is at most a problem of making a shliach on shabbos [tosafos 22b holds that the sofer and eidim aren't even shluchim, it is only a din of l'ishma that they must be appointed]. It is clear from the Rosh that there wouldn't be any problem with setting up a shliach on shabbos [from the fact that he rejects the rashbam who holds that the concern was to avoid carrying in the reshus harabim, by saying that he can simply appoint a shliach to go to the place where the gett is and give it to her]. Therefore, even if normally the gezeira against marriage and divorce is that it would lead to writing, they were only gozer on the actual ma'aseh of marriage and divorce, but not on the preliminary set up which is no more than appointing shluchim.