home mortgage usage
Can a home mortgage, in excess of $1 million, be used to refinance a commercial property mortgage? And would there be any limitation on the interest deduction?
Can a home mortgage, in excess of $1 million, be used to refinance a commercial property mortgage? And would there be any limitation on the interest deduction?

The interest tracing rules would come into effect here. If the proceeds of the loan are used to finance a business property, then the interest expense would be deductible as a business debt, not a home debt. That portion would not be deductible on Schedule A.
Home acquisition indebtedness has a $1 million limit, plus $100K for home equity indebtedness.
Should there be a written election attached to the return re: the tracing of this interest to a business or a rental? If so, what wording would you recommend.
I know of no election available to that effect. Just the fact that you are not showing it on Sched A is probably enough to satisfy the rules.
It is an actual election per Reg 1.163-10T(o)(5). Here's an excerpt from the Journal of Accountancy:
"The election is made by the due date of the return, including extension, for the year in which the election is effective, by deducting the interest on the appropriate line of the tax return. It is also recommended that taxpayers attach a statement to the tax return. See Temp. Treas. Reg. § 1.163-10T(o)(5)." --http://www.journalofaccountancy.com/Issues/2010/Jun/2010263...
And the election then applies for the year of the election and all subsequent tax years. The election cannot be revoked without IRS consent.
I also do it as colibri explains. Without this election I don't think principal home debt can be allowed the tracing rules. Although I would reckon some revenue agents would probably OK it without the election if you could show trails.
Perfect - thank you everyone - so re: the wording how would you actually word the election?
Something like...
Pursuant to Treasury Reg. 1.163-10T(o)(5), taxpayer elects to treat debt as not secured by the qualified residence and instead will deduct the related interest expense as a business expense.