I've had a think about your idea. Assuming you know what the favourite is and that its tote odds will be $3.50 to $4.50 it still doesn't make much sense to me.

I went to http://www.propun.com.au/bookmakers...ling_index.html
and had a look at tote odds compared with bookie odds for Saturdays in Melbourne & Sydney.

Here are some examples of winners:

Why would I want to take
$3.50 tote about Flying Pegasus when $4.00 is available with the bookies.
$4.40 tote about But I'm Serious when $5.50 is available with the bookies.
$4.10 tote about Dance At Ascot when $5.50 is available with the bookies.

To me a method based on backing tote favourites is doomed to fail because of the big tote unders you get on Saturdays in Melbourne & Sydney. Now if you don't get such big unders on the tote midweek it is not because the tote offers you any better value. It is simply because the bookie markets may offer you worse value.