Check your deposit account agreements. They should / probably say that any one owner can make changes to the account. If that's the case - and I've never seen an agreement where it wasn't - you should be OK with one person signing.
By way of comparison: Do you require both account holders to sign if one requests a debit or ATM card? It's the same logic.
However - and this is a big "However. . ." be sure to check the policies your board put in place when you started internet banking - whether it was the newness or a fear of the internet, some boards may have been overly cautious when they set up the original policies and now they're stuck with them.
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If you approach life with pure logic you can avoid almost all of the fun.