Insert statements using ExtractStatementListExpression

Hey,
     
The following example

int x = 20;        _ _
string s = "result = " + extract(|  int y = 10;     |=> x + y + z);
   |_ int z = x * y; _|   

my problem is i can not reference the y and z variable in the <<inner expression>>,how can i import the scope here?

please reference this:
http://forum.jetbrains.com/thread/Meta-Programming-System-705