QUICK answer is NO, NOT POSSIBLE!
explanation... 
field related is (can only be) of type the original field  is.. so if you make a relateion to a char field it can only be of type=char...
if you want selection, then you can make field related to some field selection in other model... 

Or if you need a field selection, you could make a dynamiy selection form a private method...

hope it helps.. 
 

I haven't tried it myself, but I think it is possible.  The trick lies in the fact that for a selection field is actually a char field anyway.  There are some limitation such as selection field only have a fix max length (which unfortunately I couldn't remember on top of my head).  Another trick is that you can supply a function to supply the selection list.  So, I presume that if the values in you char fields are not longer than the max length and you can create a function that returns [('name 1', 'name 1'), ('name 2', 'name 2'), ....] you may be able to make a related field as a selection field instead of char field.

It would be hard to me to guess what is the advantage of doing this though.  One reason why I would ask that is because the related field should be displayed readonly unless if the write mechanism is developed specifically to handle that.