You can't do it as you think. Background is the background so the content will be always at the top of it.
You can add padding-right and then it will create a spacing from right border.
Other way- You can add <img /> tag (which is your image) at the beginning, before any text in your blockquote and add style property float: right for this image.
Then your image will float to the right top corner and text will be around. But it requires adding of image...