I don't think you'll have much success with that approach. From what I remember you need to use the InfoBright file loader (ASCII files, or binary files if you have...
For Excel 2007 to use the FORMAT_STRING setting correctly, you may also need to set the LANGUAGE property for the calculated member - see this blog post;
I work for a large (12000 staff) organisation and our national IT manager is 3 organisation levels below the the CEO, and I can tell you now it makes life...