Christian wrote once into c.l.t.:

BLT can create (semi-transparent) bitmaps of text in arbitrary directions

Try the following:

     package require BLT
     ::blt::bitmap compose myNewBitmap "this is a text" \
         -font "Ariel 10 bold" \
         -rotate 90 \
         -justify left
     $myCanvas create bitmap 50 50 -bitmap myNewBitmap \
         -foreground blue \
         -anchor nw \
         ...


This works nicely.