You should not try and use personal expenses in Scorp to try and dodge taxes. That is a section 230 code violation. You can use unreimbursed business expense on the shareholders 1040. As far as basis, nondeductible expense general does reduce basis (not below zero) See link: good info.

https://www.thetaxadviser.com/issues/2010/apr/scorporationbasisreductionsfornondeductibleexpenses.ht... 

Sec. 1367 provides rules for adjustments to S corporation shareholders’ basis in their stock. Generally, basis is increased for items of income (including tax-exempt income) and the excess of deductions for non–oil and gas depletion over basis of the property subject to depletion. It also allows for decreases in basis (but not below zero) by each of the following:

• Distributions;
• Items of loss and deduction that flow through to and are deductible by the shareholder;
• Nonseparately computed loss;
• Nondeductible expenses that are not properly chargeable to capital accounts; and
• Depletion deductions for oil and gas property that do not exceed the adjusted basis of such property allocated to the shareholder.