The @ syntax is supported by the 8/16 bit tools (HC08/HC12).
I never used DSP56F805, so I cannot really say anything useful specific to this compiler, but I would suspect that you can place some variables into a specific section and then place this section in the lcf file.
If you do not really need a variable, just a way to read/write from a certain memory location, you can use a macro instead of a variable with any ANSI-C compiler.
#define MyVar (*(unsigned char*)0x200)
The actual code using it looks just as if a MyVar variable was defined as unsigned char, what's not so good is that there wont be any debug information tough, also the "variable" wont be initialized, of course.
Daniel