You can do it technically with no limitations under visa exemption but practically even if you spend only 1-2 days each visit every week at a certain point the IO will ask you to get the visa. For sure for a couple of months they will not deny the entry but be ready to be questioned and have return ticket ready to show. At that point better to apply for a visa to avoid problems but the question will remain as you will travel too frequently and for super short visits
simply going to immigration office with printed tm30, copy of visa/exemption stamp page, copy of data page and 2 photos. 500 baht for express service or FOC for standard service