Hi,

I find it easy to automate everything with the exeption of 
>> moving adequate data back to diskpool,

This is because you only can move all data from volume to disk stg, which is
notoriously smaller.
So you will want to watch the move process and cancel as soon as 
disk stg becomes almost full. 
OK, OK,  this could be automated as well, but...
All that scripting is not worth the work.
Short and simple paper-written procedures 
for operator might be convenient enough.

But understanding backgrounds of your problem,
I suggest another solution: 
let your customer purchase another tape drive. 
No, not LTO drive, a cheaper one instead,
maybe DLT1 which is only some 60.000 CK worth
or even cheap DDS3 tape (but remember: you wil become what you pay for)

Define only your backup stg on this drive, use it for nothing else,
eventually with the exception of full database backups.
This way there will almost no tape changes be necessary on this manual
drive,
no obscure workarounds will be necessary, 
and the customer will not be in the risk of single drive failure.

If it helps you to sell, 
I even could you let you know the # of my bank account :)

regards
Juraj Salak