I didn't follow the previous discussion, but here's a ready-made macro
solution (from 2004):
http://www.mf.uni-lj.si/ibmi-english/biostat-center/programje/excel/BlandAltmanPlot.xls
For several other Excel solutions for statistics, related info and links,
visit our website at
http://www.mf.uni-lj.si/ibmi-english/biostat-center/index.html
and follow the link on the left to Software (and scroll down to Excel
workbooks).
Regards,
Gaj Vidmar, PhD
Univ. of Ljubljana, Fac. of Medicine, Inst. of Biomedical Informatics