I don't get it. Are you asking for the power-ups as usable items, or as bricks? In the first sentence you say items, in the last you say bricks.
If you're asking for them as usable items, there are already substitutes:
1. Events that change playerscale, or the "Mega Mushroom" item that was on RTB
2. AlphaColas. There is an invincibility cola, it even plays the Mario invincibility star theme when you have it. Or, some clever eventing with an invincible playertype or Event DisableDamage.
3. Magic Fire in the elemental spellpack that was on RTB.