[plt-scheme] Syntax Reader and Macros

I am having two problems with the way syntax objects are read. I 
am currently trying to evaluate expressions found in the middle 
of strings, using the #%datum macro. The first problem is that 
when I use read-syntax to get a syntax object representing the 
expression, I can find no way to attach it to the correct 
lexical environment. I get errors on anything I do, since it 
seems to be attached to an empty lexical environment, with not 
even #%app, #%datum, or #%top defined. If I use read and 
datum->syntax-object, I can attach it to the right lexical 
environment, but I lose the syntax location information needed 
for syntax coloring and error reporting. How can I attach an 
already built syntax object to a particular lexical environment?

Also, when I read characters and expressions from a syntax 
object converted into a string, I read one character per logical 
character in the string. In the code, however, a character such 
as a newline can be represented as a newline directly in the 
input, \n, \12, \012, \xA, or \x0A. This makes it rather 
difficult to predict how many characters in the input file 
correspond to one character in the string, which makes it hard 
to calculate offsets for highlighting and error reporting in 
various parts of that string. Is there any way to tell how many 
characters one character in a string corresponded to originally? 
Would it be possible to attach some table to string syntax 
objects that tells you which characters in that string 
correspond to multiple characters in the source? Or does anyone 
else have any other suggestions?

Thanks,
Brian