Tax on joint interest income for couples living in different states?

I live in CA and my wife lives in NJ. We have a joint account with a CA credit union. Now CA only taxes the interest of CA residents. Since my wife's non-CA income also contributes to this interest, how should I split it for tax purposes?Tax on joint interest income for couples living in different states?
If your checking/savings account is community property, then half of the income is yours and half is your spouse's, for California tax purposes. If not, then any reasonable allocation based on the source of the funds in the account would probably be accepted.