This is a pretty old question, but based on its unanswered status and number of up votes and views I thought I'd take a crack at it. Based on your question and the additional comment about doing the conversion on a programmatically on a Linux server, I did some hunting around. There is a Ruby library called ruby-pdf that does colour conversions for handling PDFs. In the docs for the library's colour tools it discusses using the tools for conversion. Interestingly, there is this tidbit:
# Adobe PDF Display Formula
r = 1.0 - min(1.0, c + k)
g = 1.0 - min(1.0, m + k)
b = 1.0 - min(1.0, y + k)
See here for the reference: http://ruby-pdf.rubyforge.org/color-tools/doc/classes/Color/CMYK.html
Note this comment: "Converts the CMYK colour to RGB. Most colour experts strongly suggest that this is not a good idea (some even suggesting that it’s a very bad idea). CMYK represents additive percentages of inks on white paper, whereas RGB represents mixed colour intensities on a black screen."