You are not giving enought details (for example: what is blend mode during rendering to rendertarget surface?)
There are multiple ways to archive wanted behaviour and without knowing why at all you need additional renderterget surface (and what it should contain) - it's hard to provide to you most suitable algo.

One of the ways:
(1) set S=ONE D=ZERO / render to rendertarget surface. - now RT contains the copy of your texture.
(2) render to backbuffer as in your first alg, but using newly genereated RT texture.