Unfortunately it will not work that way.
The capital losses first get applied to other capital gains, then after that up to $3,000 can be deducted and will reduce the other income on the return.
But no more than $3,000, so if you took $10K out of the 401K or to a Roth, the $3,000 of capital losses would be the same regardless of what you did with the 401K.
