This system is still unsafe. Assume Bob would be a cheater. He could create fake transaction sending his CPU to himself. Then, he could silently create transaction sending BTC to another address and broadcast it as soon as Alice release her honest transaction. Then, Alice will lose both coins, because her reverse transaction would be treated as "double-spending attempt" by the BTC network.

Even creating another type of transaction is still not sufficient. For example you can safely create a message that lists all inputs and all outputs for both coins. But even if such message would be a valid transaction in both networks (if signed by all parties), it is still vulnerable to "race attack" when honest party releases its coins and dishonest party creates another transaction moving funds to its own address and broadcasts it (making any next transactions as "double spend attempts").