One way, might be the easiest is to change the list that populates 'Block List', adding spaces to the nested block
So you might have a line like this in your LISP:
(start_list "lst" 3)(mapcar 'add_list BlockList)(end_list)
Where BlockList is your list of block, might be
(setq BlockList (list "BLOCK-1" "BLK-1" "BLK-2"... "BLOCK-2"))
Which you could change to be
(setq BlockList (list "BLOCK-1" " BLK-1" " BLK-2"... "BLOCK-2"))
I don't think you can do the indenting with DCL, has to be done before then.