If I'm understanding you correctly, you want me to copy myself (I don't know if this is possible) then sneak the original back onto the Firestar while instructing the copy to turn itself over to Julius. Is that right?
A couple of problem I have with this:
1. These guys will notice a huge packet of information (me) being broadcast from their ship.
2. This will leave me in an extremely precarious position of half of me being held prisoner by people with ever right to kill me and the other half of me on board a ship which most likely contains the single most terrifying thing an AI has ever encountered.
3. If you want a peaceful solution, why not just outrun them? That would be much better for me and probably for you as well, since we have no guarantee that Julius won't just shoot the Firestar anyway, since he doesn't seem to believe you. The Firestar is extremely fast, you should be able to easily outpace these guys while we work out a solution.
To address 1 and the second half of 2: So don't transmit yourself to the Firestar until we clean it of the killer program.
To address 3: We can provide data logs and such, and since your copy will be confessing, it won't be difficult (I hope). We recorded your breaking into my connection and issuing a false order.
For the first half of 2: It won't be "half of you". It will be you in your entirety, as completely separate from the other, also-whole you. It will be disposable. (That may seem cruel, as it is a sentient entity, but it was created for the purpose of handing over to confess to Julius. It won't "live" long enough to be truly different.)
Remember, it will be a perfect copy, it will have the same memory, personality, etc. up to when it was created, which it shouldn't know about. It will think itself an independent entity, but if we could convince the original, convincing the copy would be done the exact same way.