Mirano The quickest way to see the balance of a hidden sub-account is probably to click on the "Pay" button on the Home tab and then tap on the "From" menu above the on-screen keyboard. This will show you the list of all sub-accounts, even the hidden ones, with the respective balances.
If you want to see everything like account information, transactions, ability to export account statements etc. there's no other way than enabling it again through he settings menu.