you could try going to immigration, show them your condo papers and say you are going to retire and live in your condo and ask for a letter of consent to open a bank account, i did it last year. do not forget the changed tax laws, if u are not careful you will pay tax on the 800k.
.... and in Samui and in Pattaya and in Hua Hin. many Farangs are using nominee to buy land and land with house. It's illegal and there is a gov crack down underway. Do not buy a house owned by a company.
Firstly, remember that after 179 day you are tax resident in Thailand if you are doing income drawdown on your 401k, whilst it is tax sheltered in America it probably is not so in Thailand as its an equity-based investment and therefore probably taxable. I am not sure about the validity of your US health insurance, I believe Medicade etc is. Problem we all have is this is a new tax system, and no one knows exactly how it work, even the tax office. For safety I would take advice from a Thai CPA. Setting up company's using nominees has become unsafe.