@Ren9,
No, it is not possible to see the discounts without looking at the listing itself.
However there is an alternative:
Select in the search as dates a period of 28 nights (the minimum for monthly discount).Then the accomodations are filtered out who do not rent for min. 28 nights. On the map you are shown the nightly prices, but on the row of listings you see the same price at each listing, and right underneath this price you see the price for a 28 nights stay. Click on the small "questionmark" next to it, and you see the discounted nightly price.
Best regards,
Emiel