Assuming everything you say is true (I don't know what a CRUT is, but I do understand IRAs), then I don't see any way out of paying tax on most of the Roth conversion.
First, it's not a backdoor Roth, it's just a simple Roth IRA conversion. If you convert any amount from a traditional to a Roth IRA, that amount is taxable income and included in your AGI. Assuming you have some kind of offset that can offset 30% of your AGI, you would still pay tax on the rest. If you converted the entire $1M all at once, you would owe about $400,000 in taxes, of which you could offset 30%. If you spread it over 5 years and converted $200K per year, you would owe about $70,000 per year of which you could offset 30% and pay the rest.
Be aware that, in addition to income tax, you will pay net investment tax if you convert more than the threshold amount (including your other income).
https://www.irs.gov/individuals/net-investment-income-tax
So the tax bite could be quite high.
