Even with a visa from the Myanmar Embassy, travel through most of Shan State is restricted to foreigners due to rebel activity. Onward travel from Tachilek is via aeroplane to Burmese controlled areas only.
BUT, on that 14 days card from Tachilek Immigration, you are allowed to take a bus north to Kengtung, the principal town of Kengtung township. Here was once part of the Lanna Kingdom, and is home o the Shan subgroup the Tai Khun.
Then from there you are allowed to take a bus north east to the border town of Mong La, or "Shan State Special Region 4". Run by the Mong La Army (National Democratic Alliance Army-Eastern Shan State), this city runs on Chinese electricity and Chinese Yuen, and serves mainly as a Sin City for Chinese tourists. Gambling, prostitutes, Tiger meat, you name it, they got it.
They like to cut the corners off cancelled or expired passports the send it back to you, should maybe tell them you've found it and ask them what to do with it.