The only way you can split residential finance costs is if the mortgage you hold is a joint mortgage. If the mortgage is solely in your name the person liable to tax on interest is the person receiving or entitled to the income.
Generally, the person liable to tax will be the person who is entitled to the interest, the beneficial owner of the interest bearing account or other source if interest. You can see guidance here:
SAIM2400 - Interest: taxation of interest: the tax charge