Yes it can not be done, i use CW. for the O-X you need the medical certificate and a police clearance certificate from your home country i tried agents and they all said no, one did quote me 40 000 baht but then said no.
I received mine through embassy in home country, now remember the O-X visa is a 10 year visa, 2x5 years, and it gets worse the MFA website states 3 million, but after 1 year can go down to 1.5 million, immigration say no must be kept at 3 million, also the MFA website states that an O-X can be converted in country to another type of stay, i was told no, i questioned it, showed the printout from the MFA website, they simply said those are not our rules, ask your embassy why they wrote it and that was the end of conversation. when i went to get my second 5 year, they said i needed to update all the documents that i used for the initial visa.
I can imagine all sorts of issues later on with the DTV visa as the holders will not be dealing through the MFA, but with the rules immigration decide to use