Yes absolutely. You do this outside of the eWallet app:
Run the Settings "app"
Scroll down until you see eWallet in your list of applications, then tap on it
Slide Lock on Suspend to the on position
You may also want to set a shorter timeout for eWallet (see "Set eWallet to lock automatically" for details.) Alternatively, you can always click the lock icon to lock your wallet when you finish with it.