Hello welcome to the boards!
This is actually a subject that has come up a few time so for some alternative takes on this you might start
here
and
here
You might see references to TG aka
Technical Grappling. This is optional extra supplement for grappling in general but it also covers armed grappling and caters nicely for this kind of attack. I think it is excellent, and I think it helps, but it is not required for doing what you want to do.
Right OK on to the suggestion. I think your right a telegraphic All out Attack including a combo will do the trick nicely here.
I wouldn't worry about invoking tip slashes. It's not what you really doing here, you're just sawing away at this chap's neck with a blade that already in there. Not trying to catch him with the very end of your swinging blade.