If you have a list of Load ID's, and you're on one of the UNIX/Linux platforms, and all the Load ID's are for one Application Group, you can iterate over the list with a 'for' command in the shell:
for LOADID in `cat LoadIDs.txt`
do
arsadmin unload -u admin -p password -g ApplicationGroup -L $LOADID
done
If you have more than 1 Application Group to unload, you'll have to break up the LoadIDs.txt into many files, each specific to one Application Group, then run the 'for loop' for each. (If you're adventurous, you can put a database query inside the loop, and automatically determine the Application Group name for each Load ID.)