Stephen's right about it being basically doable, PeteJ. You might want to take your double stops with half notes and clip them down to eighth notes in unison with your treble lines in the fourth system on page two. Given how collosal the decay rate is on the guitar's tone you can do this and any informed audience will be generous enough to "fill in" by way of aural memory what the implied note values should be despite the guitar's decay rate.
You could also do something similar with the quarter note values against the eighth note melodic lines. It's the kind of simplification of texture that won't really be cheating given your voice-leading in the score, but it will make it easier to play fluently. When I compose fugues on the guitar I keep this decay rate in mind and incorporate it into the textures I write. If I were writing a polyphonic piece for choir things would be different but if there's anything to be learned from Baroque compositional practice it's that tailoring your stylistic approach to the real world limitations of your executing instrument is no bad thing.