Most Thai Embassies / Consulates allow the proof of 65,000 Baht equivalent per month for 12 months with proof from home bank that such an amount of money past through your bank account even if the money only stopped there on the way to Thailand.
Daniel, when you get stamped in at the airport in Bangkok... Double check the dates you have been stamped in for.. One year from the day you are stamped in.
In over 5 years of monitoring thousands of Visa / Extension related posts on various venues, I cannot recall one incident where an I/O allowed the use of two accounts to meet financial requirements when using the 800K cash in the bank method. And I have an excellent memory.
I think the plan to use two accounts is an unnecessary waste of time.