Yes, your solution probably removes perl from %PATH% after the BEGIN block. I can think of two reasonable answers at the moment: (both untested)

1. Move use Tcl; into the BEGIN block and use local when adjusting $ENV{PATH}.
2. Prepend the Tcl directory to the PATH with $ENV{PATH} = $pathTclBin . ';' . $ENV{PATH}; instead of replacing PATH. (The PATH separator is colon on POSIX and semicolon on Windows.)