I would have a number of comments in regards to your posting.
#1 - I think you need to go back to provider (Wimax) and ask them why they say you need a Q-in-Q packet? Did they tell you what they are doing with the packet? Did they tell you what outer (S-VLAN) value to use? At best they could only look at the outer tag, so how would they know whether or not an inner tag was there to start with or not? Did they tell you what dot1q ethertpye value to use for the outer tag?
If the answer to these questions as No, then I would suggets they are blowing the provebial smoke up your A$$.
#2 - I assume the connection from SRX1 and SRX2 to switch 1 is also some sort of WAN (geographically disperse) connection. So what sort of physically connection is this? Same provider, dark fiber, etc., etc.? In order to not worry about loop avoidance why can't these links be made into L3 connections? At the same time, the connection between the SRX's is L3 (yes) in which case you have no L2 loop to worry about, yes?
#3 - The Ingressing packets from CPE1, (EX2200 or router or what??) should be tagged to start out with, meaning that ingress port on the SRX-1 is also tagged, and not an access interface, no?
I might suggest you go back to whomever your purchased the SRX's and EX2200 from, and if they are indeed a Value-Added [juniper] Reseller (vs say CDW or Best Buy or Amazon) and get them involved for best way to configure and set-up this network design. IMHO you need to figure out what are the design goals, what network restrictions may exist (Wimax or other SP's) and how best to design and then worry about the configuration after all this is determined.
Just my 2 cents worth. Good Luck.