Officially you don't. Thank big movie studios for that!
When you connect an analog receiver or a digital one without HDCP, there is a resolution limit in place. I can't get exact numbers right now, but it should still be better than regular DVD.
There are ways to circumvent the issue, but the fact that you don't have HDCP enable output makes it more problematic.
For HDP enabled sources there are devices such as HDFury for example which will strip out HDCP out o the video stream and enable analog connections, but that won't work for you since you don't have digital output.
So what you need is to remove the "protection" before it gets to video output. There are several ways to do that.
There are programs like for example AnyDVD HD which are capable of removing the protection.
Another way is to remove the protection yourself using various open-source utilities. For example MPlayer has some support for Blu-Ray disks and there is a guide for it too.
The problem with these two ways is that you need to copy data from BD-ROM to HDD and that will of course take up HDD space and need time.
I don't know of any way to decrypt and play disks on the fly with hardware which has no official support.