Vista - Any way to merge tiff files in Vista Fax and Scan?

I have an HP3050, which is a multi-function centre with a one sided
scan and document feeder.

Obviously it would be enormously helpful if I could merge TIFF files
together, then I could scan the front pages of a document then flip it
over and feed it back in to do the back side of the documents and then
the computer merges the two series of scans to create a "duplex" scan
with all the pages in the right order.

Neither HP's software nor Windows Fax and Scan seem to have that
functionality, unless I'm missing an option somewhere.

So how do others do this?

Travis