not true... depends on which consulate you are applying to for the 60days tourist visa. For example the Thai consulate in Canada does require onward travel ticket when applying for tourist visa.
each Thai consulate will ask for different things. There is also things that are lost in translation. When I applied for a METV last year the consulate that processed my application wanted proof of funds going back 6 months. So I had to send my bank statements for the last 6 months. In my case they wanted to see at least a balance of $7000.
I know people have been able to do it but it's because they didn't receive the e-visa on time and already entered Thailand using the 30days exemption stamp.
Apply for the 60day Tourist visa from your home country. Once issued it will be valid for 3 months meaning you have 3 months to use it. When you arrive in Thailand the first time don't use the visa and enter with the 30 day visa exempt. When you go to Bali for the week and re enter Thailand use the 60day Tourist visa. (Should be still valid but check the dates and enter before it expires) .
After you submit your proof of accommodation on the e-visa system the affiliated Thai consulate will send you an email for any further documents they want from you. In my case I received the email 1 week after I completed my e-visa application. They asked for an accommodation booking of at least 7 days. (Thai consulate Ottawa Canada)