This was discussed for a while on the -hackers list. IIRC, if the feature
was enabled, a fairly small (4Mb) chunksize could be set, and the chunk that
was being written when EOT was encountered would be re-written, in its
entirety, as the first chunk on the next tape. Re-assembly could still be
done with shell tools. 

The next level of this (which I thought was very interesting) would be to
allow AMANDA to write chunks of backups as they become available, without
waiting for an entire DLE to be ready. This would allow the tape to start
writing almost immediately, an advantage for sites with lots of large DLEs.
There was a resolution to the restorability issue, I think with a small
package of tools at the beginning of each tape, but I'm not sure.

I think 2.4.4 lays the groundwork for some of this also, but for now the
answer is to split the DLEs so they fit.