Wombat

Of course it's possible.

eg Market is as follows and you don't like number 2, but also lay 1 & 3.

1 - 6.0 $20 payout $120
2 - 3.5 $120 payout $420
3 - 4.2 $40 payout $168

If 2 wins, you lose $240
If 3 wins, you win $12 (less commission of around $0.60c)
If 1 wins, you win $60 (less commission of around $3.00)
If any other wins, you win $180 (less commission of around $9)

If you didn't realise this until now, I'd tread very carefully on Betfair.