I'm not sure if this is what you want, but you can include specific fields inside headers. The only thing you have to do is update fields for the header and the document separately
If you have today's date within the document and you want to include it in the header:
If this date changes just update the field within the header using Ctrl+A and F9
This works with any field; all you have to do is make sure both the document and header fields update each time. Word treats each block separately, but I'm sure it's also possible to automate field updates with a macro as well.