Shambles, there is a way to make a guitar sound a lot like a bouzouki. Tune it (from low to high) CGCGCG. This tuning uses the same intervals as the common ADAD bouzouki tuning - just lower and with an extra string both above and below where the bouzouki stops.

I actually prefer it to playing the bouzouki for a number of reasons. It is easier to reach the higher notes in many tunes because they fall in first position on the high G string instead of having to go up the neck on the bouzouki's high D. You can play many tunes in higher and lower octaves by just changing the string you start on instead of changing fingering positions. The bass notes add a dynamic that the bouzouki does not have.

On the down side, guitar E strings do not like being repeatedly taken up to G and then back down to E. A new 11 guage string will break after two trips. An extra guitar that can be dedicated to this tuning and strung with custom guage strings is a good idea. Also, not too many Celtic tunes are played in C so the first two frets are pretty much always on the wrong side of the capo. For most guitars, capoing at the seventh fret (key of G in this tuning) is about as far up as you can go without the heel getting in the way. So, tunes in A pose a problem. I solved the problem by buying a Wechter Pathmaker which is an acoustic double-cutaway on which the neck meets the body at the 19th fret. Capoing at the 9th fret is no problem (but it does get to sounding more like a mandolin than a bouzouki). I do occasionally tune my Guild 12-string to this tuning and it sounds remarkably like a bouzouki, but it usually involves a string sacrifice as I only have one 12. If I ever see a good deal on a used 12-string Wechter I'll doubtlessly succumb to another bout of G.A.S. (Guitar Acquisition Syndrome).