I'm not sure but I think some commands can work together.
You can insert block at station of a polyline. Before executing you will get a question if you want to rotate the blocks according to the polyline. This command is found in "Draw from coordinates", Type "Block at station/offset from polyline"
What station does my block have? To get station of blocks beside a polyline you could use "Text, Circle and Block station/Offset from polyline to Excel" found in Miscellaneous.
So first you need to get the station and offset of the blocks to excel. Then you paste these values into "Draw from coordinates" and answer YES to rotate while inserting. (Plot the inserted blocks in a different layer) You should now end up with rotated blocks according your polyline.
Hope this helps
/Lars