2 Separate States

my wife and I have a
joint investment account that generates about $40,000 annually as ordinary dividends
and because we file a joint federal return, that amount appears as adjusted gross income.  
 
If I were to file a Wisconsin Tax Return as "Married Filing Separately", half of that
$40,000 income rightfully belongs to my wife and if would be assumed that she would report half of that amount on her out-of-state return.
 
Therefore, where the Wisconsin Income Tax Return asks for the amount appearing as Adjust Gross Income ($40,000) on the Federal Return, I would only be responsible for half of that amount.  How do I clarify reporting less than what appears as adjusted groos income on the Federal Return with the Wisconsin Department of Revenue?