The ball spawns in front of the 'finish' where it needs to hang for 3 seconds.

Place four bombs stacked on top of each other about 2/3 downwards on the platform in the center, aligned with the position of where the ball will roll.

Place your fifth bomb just before the ball will land when it spawns.

I included this awful paint drawing to make it more clear.



After placing the bombs press 'R'. Now you can activate the bombs and are no longer in editor mode.

Quickly double press 'R' so the ball is in front of the finish and the counter starts going down.
As soon as it hits the tile your bombs are on, active the 4 bombs practically together. The ball should fly straight up nearly reaching the top, keeping the counter active and counting down.
When it falls down again and is halfway the finish, active your last bomb. This should send it back to the top again and by the time it reaches the bottom your should have reached the level.

With this setup it took me about 30 tries before I had the timing right. I hope this helps someone!