Simply set off the line blaster every single move...
Clear the row between the bricks as soon as possible, so that it becomes a row of metal boxes.
If the line blaster is level with the metal boxes great, if not, don't worry. Keep setting it off and it will build up your paint quickly (each three or four moves)
When you have paint, use it to lower the blaster to the row of metal boxes.
All you need to do is keep blasting that row and Pets will fall.
As soon as a Pet has cleared the last column, and moved to the left, another will fall in the next move. So keep them moving down by clearing the row between the bricks.
When you have a few Pets waiting, blast the bottom row to have it clear to let them free, then keep working on the row of metal boxes to get the remainder of the Pets.