I do not have the answers to your questions but I can try. First I think it might help if you told us what species you are talking about. From my small experience with overwintering TDS I can say that some can take it well and some don't.
1- I suppose the tree can be forced into dormancy : decreasing light period and decreasing temperatures might be able to do the trick.. (placing hte tree in a cool dark room). The question is if you're patient enough to go back and fourth with the tree twice a day ? What I would most probably do is to place it directly, not outside , but somewhere where the temps are pretty cool (not freezing but just a little bit above) and let it do its thing (while making sure that the soil is not soggy).
2- Photoperiod in this case will not be the only factor in breaking the dormancy. Air and soil temperatures play a big part as well.
3-I think that depends on the species as well and also how well prepared it is : an outdoor (hardy) plant will be able to prepare itself for subzero temperatures, while the same plant that has been grown indoors will just freeze if placed outside all of a sudden.
Two questions I have : has it kept its leaves or not? and do you see new buds forming yet? Many tres fail to survive because they need the cold rest in order to produce new buds. But if the buds are already forming, I think you have great chances that it survives, even without the dormancy.
HTH