I have had the same situation as you. We only have one server being backed
up with ADSM. Full Incremental is a nice policy for most restores but
sometimes you want to have a complete point in time for disaster recovery.
I tried making a copy pool. I figured I could copy the default storage pool
to another pool and remove those tapes. The only way I could get that to
work would be to define a disk pool and make the tape drive a copy pool.
The we have our single server set up is to use  the tape drive as the
default storage pool. SO, no luck there.
Then I found tapeutil. A tape drive command utility that lets me mount
media in my robot tape drive. I schedule a cron job to do full backups with
two cartridges in my magstar 3570 tape drive. The only drawback to this
setup is that ADSM may not know that these two cartridges are being used
for this . ADSM may try to use them as scratch. I suspect that I will have
to assign these two cartridges a separate pool to prevent accidental use.
As you can see. ADSM is very powerful, if you do things the ADSM WAY.
Otherwise, you have to make it up as you go along. I would be interested in
what kind of solutions you may devise.