You can use the following method, which is not perfect but works if hotel have avaiability for all days within the next xx days:

1)choose the hotel
2)provide dates for duration of stay e.g. from today +45 nights
3) the site will list all avaiable rooms and show the average price for the whole time frame
4) click on the reserve button for the room you want
5) now if you scroll down you will find on the very end of the page a calendar, every day field of the calendar shows the rate valid for this certain day, from this data the average price is calculated

Sorry for my clumsy english...