Can you sacrifice on Temporary Death?

Yes, you can.

When a unit with Temporary dies at the start of your Beginning Phase, it creates a chain, which allows you to play [Reaction] speed abilities and effects in response to that death trigger. If you control a card that requires a sacrifice as a cost to activate its ability or play it, you can use that unit as the sacrifice in response to the Temporary death trigger before the unit is removed from the board.

According to RiftJudge FAQ #6422, Temporary is a triggered ability that creates a chain, allowing players to respond with [Reaction] speed effects.

How it works:

1. Trigger: At the start of your Beginning Phase, the Temporary ability triggers and is placed on the chain.
2. Closed State: Because there is an item on the chain, the game enters a "Closed State."
3. Response: You can use your [Reaction] speed ability, paying the cost—which includes sacrificing the unit—to place your effect on top of the chain.
4. Resolution: Because the chain resolves in LIFO (Last-In, First-Out) order, your sacrifice ability resolves first. Your unit is sacrificed to pay the cost of your effect, and then the original Temporary trigger resolves. Since the unit is already gone (sacrificed), the "Kill" instruction of the Temporary ability will simply fail to find its target (it becomes an impossible instruction) and nothing further happens to that unit.

This is a common way to extract extra value from a unit that is about to die to its own Temporary effect.