CPU instead of USB-Blaster

What you try to achieve involves undocumented steps. Programming default SFL image would the most easy and is documented, cause it means performing a FPGA configuration through JTAG from an embedded processor. The embedded JRunner code can do.

The more complicated action is JTAG indirect programming, in other words controlling the SFL through virtual JTAG protocol. Virtual JTAG protocol generally is documented in an application note, the SFL specific protocol part isn't explicitely documented and has to be extracted from the SFL HDL code. Finally you have to perform each step in EPCS programming separately, there's no intelligency built into the SFL design.

For this reason, it's much easier to program an EPCS device at the AS interface directly, as cms mentioned. That's what most people do. Of course, if you didn't connect the interface in your design, you can try indirect JTAG programming. I'm sure, that it can work, but it involves a much higher effort.