Tbh, I don't think it would've been necessary to "flatten" the TCA-Xmember bushes. Recently I fitted new PowerFlex bushes in the front as well. The TCA needed some persuasion to go in between the Xmember but didn't even need a tool for that. It went in fine with the PU sticking out like you described.
I was hoping the same thing, fit the TCA and then squeeze the ARB in between but found out soon enough you can forget about that.
I fitted driver's side TCA, bolted the ARB to the body, fitted one side to the TCA already fitted into the xmember then I put the other TCA on the other side of the ARB, fitted the nut handtight and used a ratchet strap to pull the TCA into the Xmember. Tightened all the bolts up and dropped the car on it's wheels.
I personally am in 2 minds about waiting with tightening up the bolts untill the car is on its wheels. I think if you DON'T tighten it up BEFORE it's dropped you will leave play in the connection which will be cause twisting of bushes. It just doesn't make sense to me tightening up when things are under strain.