In what context does he make the remark about it being unusual? It makes a difference. Most likely he is referring to the fact that εὐλογητὸς comes at the beginning of doxologies. If that is the case, his remarks don't have any bearing on yours. You might want to check that out.
It is on p. 161-163 of:
Jesus as God: The New Testament Use of Theos in Reference to Jesus
You may get blank pages, I have them archived, but not in text mode.
Here is one sentence:
The alternative way of explaining the extraordinary inversion (on the assumption that v. 5b is a doxology to God the Father) is to suggest that
when the subject contains the dominant thought or is prominent in the writer’s mind, it may precede the predicate.
There is also a section discussing:
it forms part of a descriptive doxology concerning Christ(" ... who is ... blessed for ever").
Which would seem to be the spin interpretation, unless an awkward attempt was made to combine it with the apposition.
Waiting for some comment on Hippolytus, who looks to be saying "God blessed (is Christ)".