Index: Modules/FindTclsh.cmake
--- Modules/FindTclsh.cmake.orig
+++ Modules/FindTclsh.cmake
@@ -17,18 +17,30 @@ library is.  This code sets the following variables:
   TCL_TCLSH = the path to the tclsh executable
 #]=======================================================================]
 
+set(MODTCL_VERSION $ENV{MODTCL_VERSION})
+set(MODTK_VERSION $ENV{MODTK_VERSION})
+
 get_filename_component(TK_WISH_PATH "${TK_WISH}" PATH)
 get_filename_component(TK_WISH_PATH_PARENT "${TK_WISH_PATH}" PATH)
-string(REGEX REPLACE
-  "^.*wish([0-9]\\.*[0-9]).*$" "\\1" TK_WISH_VERSION "${TK_WISH}")
+if(MODTK_VERSION)
+  set(TK_WISH_VERSION "${MODTK_VERSION}")
+else(MODTK_VERSION)
+  string(REGEX REPLACE
+    "^.*wish([0-9]\\.*[0-9]).*$" "\\1" TK_WISH_VERSION "${TK_WISH}")
+endif(MODTK_VERSION)
 
 get_filename_component(TCL_INCLUDE_PATH_PARENT "${TCL_INCLUDE_PATH}" PATH)
 get_filename_component(TK_INCLUDE_PATH_PARENT "${TK_INCLUDE_PATH}" PATH)
 
 get_filename_component(TCL_LIBRARY_PATH "${TCL_LIBRARY}" PATH)
 get_filename_component(TCL_LIBRARY_PATH_PARENT "${TCL_LIBRARY_PATH}" PATH)
-string(REGEX REPLACE
-  "^.*tcl([0-9]\\.*[0-9]).*$" "\\1" TCL_LIBRARY_VERSION "${TCL_LIBRARY}")
+
+if(MODTCL_VERSION)
+  set(TCL_LIBRARY_VERSION "${MODTCL_VERSION}")
+else(MODTCL_VERSION)
+  string(REGEX REPLACE
+    "^.*tcl([0-9]\\.*[0-9]).*$" "\\1" TCL_LIBRARY_VERSION "${TCL_LIBRARY}")
+endif(MODTCL_VERSION)
 
 get_filename_component(TK_LIBRARY_PATH "${TK_LIBRARY}" PATH)
 get_filename_component(TK_LIBRARY_PATH_PARENT "${TK_LIBRARY_PATH}" PATH)