I have a spreadsheet with multiple references to an external sheet
located on a website.  

Every one of these cells has the line something like:

='http://webpage.aspx/[EXCELBOOK]FirstPage!$A$1'

with the specific A1 reference different each time.  What I would like
is to be able to use something like INDIRECT to simply write

='http://webpage.aspx/<<LOCAL CELL REFERENCE>>FirstPage!$A$1'

So that I could change the local cell reference to the name of
different workbooks and it would change to the A1 value of the
workbook of that name.

I know you can do

=INDIRECT(CELLREFERENCE)

but CELLREFERENCE needs to be a workbook that is open, which means I
have to manually open the workbook first, which defeats my purpose.

I hope I was clear enough...

Thanks for any assistance in advance.