That option being just using his gravity to push the strings outwards. We have seen he can do that with his flying rock. We have also seen that he can effortlessly destroy a rock with the force he creates (which actually means nothing seeing they already did that kind of thing in the Kuro arc :D) but his force is definitely high enough to push away some bladed strings. Also Pica can control the surface of the Island? My guess is Isshou kan too…
Should read my birdcage theories earlier in the thread.
I mentioned how the birdcage could actually be in a sphere shape meaning wherever Issho will move it, things will get sliced. I don't think it's a basic semi sphere.
–- Update From New Post Merge ---
I'm arguing that he will have some really important side job. Taking care of Birdcage, in this scenario, is a side job. Main one is taking care of Doflamingo and his subordinates.
But Doflamingo is right next to the headless Doflamingo which is the source of the birdcage. So to get to it you must reach DD. In this case Issho has the main and the side job.