How would you do that? The read out will be meaning full if it matches the target. I will have to set the film curve to linear and furthermore apply a curve to bring the black and the white patch into the range of the target values. After this I can start to try to get the colors into sinc via the read outs. I did that. The result was not nice, because while you tweak here you untweak there. I guess you know what I mean. (BTW the read-outs from my c1 v6.0.1 copy are meaningless - I filed a case)
in this case (tweaking the generic profile of the 5D2) you should set the film curve to "film standard". The linear curve is only useful if you start to create a new profile from scratch.
As to the "how to"...
1.) I'd shoot a color chart
2.) load (or create) a gretag chart with the correct Lab values, convert the file to your desired working space in Photoshop
3.) read out the RGB values from the info palette in photohop
4.) set C1 to the same working space
5.) tweak the colors in C1 so that they match the respective RGB values of the gretag chart in Photoshop
... but, as you've said, it's very difficult if they all have to match dead on ... so if this is your target a decent profiling software is the way to go (that's what it is for after all).
Don't know about the workflow in Argyll, sorry.
edit: "(BTW the read-outs from my c1 v6.0.1 copy are meaningless - I filed a case)"
you are right. The read out values refer to sRGB (for some reason).
Oh man ...