At this point, no dates are for sure. I'd say you have at least a month. I'll keep in touch with you and everyone else regarding dates.
What we should probably discuss though is what notes you'll be playing! One option is to play the melody, another option is to play some sort of harmony or accompaniment part, or perhaps a combination of both. For now, let's put you on melody (let me know if you want sheet music!). I'll work on composing an accompaniment/melody violin part for the song and I'll let you know how plausible it will be to work into the song.
For sure though, we can at least have you play the melody. We'll go with that for now and I'll get back to you with cool harmony stuff in the near future. Again, if you want sheet music for the melody, I can get it for you pretty quick. Just let me know. B)
Out of curiosity, what is your skill level on the violin? Basically, I need to know what sort of difficulty limits to concern myself with when composing the new part.
(Geez, if we had a few more musicians, we could perform the entire song using live instruments! We need a drummer, a keyboardist (I can do that) a cello player, a guitar player and an english horn player the most

Anyone?

French horn player could be useful too: Adam?

)