...That.
Okay.
That works. 
Very good show. 
Maybe it was the blood of the mages who bound them, rather than their own blood? Or part of enslavement involved dragging a spirit down into the physical realm, (giving them blood and bone and all that good stuf) then using their own blood to bind them outside of the summoning circle?
It seems like the most likely answer for all the Fade shenanigans.
Maybe, but here's the thing about that.....
....Solas said partaking in blood magic reduces your connection with the Fade. So, I don't know that the nobles or Evanuris of Arlathan would would have used their own blood for such rituals right? Maybe, but it just seems to lean away from that.
However, there are two sources of blood that would be very linked to the physical world and probably worked out pretty well for such purposes.
One of them being Titan blood. The other is Dragon blood, but I lean towards the idea that they must have used Titan blood for such things if they did. Main reason being, I bet the Evanuris/nobles didn't start using valalslin until after the war with the Titans. That is, if the war with the Titans is the war Solas referred to in the end dialogue. It works out pretty well for a timeline of events then.
1.Spirits start taking the shape of elves. Very powerful spirits such like Elgar'nan and Mythal being among the first. Other's followed in suit.
2. Titans didn't like what spirits were doing taking shape in the physical. Not to mention that these elves would have been able to alter reality through magic.
3.Elves-Titan war happens and elves are victorious through the leadership of the Evanuris.
4. Elves discover lyrium and its uses. You start having incidents like Andruil and her Void armor for example.
5. Gradual progression of Evanuris into godly status. Somewhere along the line someone(I bet June, and not a joke this time) figured out how to use lyrium for blood writing runes onto followers in order to bind them to the real world. He even made them look nice and basically spell out his besties names. I think this is the Great Favor of Clever June to Sylaise. And the rest of the Evanuris.. Shot in the dark, but it works here. Probably some kind of gradual process. Like everyone getting a RFID chip and such.
All this leads to some Evanuris acting a fool after a while, then Mythal tries to speak out and I think she must have summoned Solas around that point. Then Solas started his whole rebellion stuff.
It's missing some serious stuff and it's late but....that's kind of what I think happened.
BioWare will most likely reveal something in some months time that destroys everything I just typed.
Such is the way of this fandom.