I don't see an option for Delphi 2010 when updating to 5.5?
Sorry, FlexCel 5 supports only XE or newer.
While we only need the functionality from D2009 (unicode, generics, etc), the truth is that D2009 and D2010 compilers are so buggy they make compiling FlexCel impossible. We make a big use of generics in FlexCel 5, and both D2009 and D2010 will crash with thousands of internal errors when doing so.
To be fair XE to XE3 still have buggy generics support, but at least we can workaround the bugs. In 2010, the number of internal compiler errors is so big that it is impossible.
I wish I had a better answer to this post, but this is what I can say.