As your visits to Thailand using visa exempt entries, increase, sooner or later an Immigration official will decide that you are no longer a tourist and will deny you entry.
I have actually used the Doi Saket Bangkok Bank branch to assist a number of people to open bank accouts successfully. Why give away 5,000 thb when not needed.
You should be able to open a bank account yourself, even if you are on a tourist visa or visa exempt stamp. All banks have different requirements. All branches have different requirements. Even within a branch two staff members may give very different answers. Find a branch of the bank you want (I use Bangkok Bank in Doi Saket), in an area with lots of foreigners. Go to the bank with your passport and a friend who holds an account at that branch. Have 100,000 thb to deposit. Should work but many banks/branches will also require a certificate of residence from Immigration. But instead, you could offer a letter from your hotel/ hostel/ Airbnb/ friends house stating that you stay there. Doi Saket Bangkok will work with that.
.
Thailand to implement stringent compliance regulations for new bank accounts - Thailand Business News (thailand-business-news.com)