I found a valuable discussion of 2 Corinthians 5:19 in V.P. Furnish's Anchor Bible Commentary on 2 Corinthians. The discussion spans about three pages (pp. 317-319), so I will merely sum up some of the main points here.
ὡς ὅτι: The Latin Vulgate gives this phrase a causal sense, treating it like ὅτι. It renders ὡς ὅτι as QUONIAM QUIDEM ("since" or "because").
Others think that ὡς ὅτι (in 2 Cor. 5:19) is epexegetical and that it should be rendered "namely that" or "that is."
Kasemann construes the ὡς in this passage as transitional: he thinks that ὅτι introduces a quotation. Furnish concurs and therefore suggests the translation for ὡς ὅτι: "As it is said."
Concerning θεὸς ἦν ἐν Χριστῷ κόσμον καταλλάσσων ἑαυτῷ, Furnish makes the following points:
(1) One may read the verb ἦν independently of the participle ("God was in Christ, reconciling").
(2) The construction in 2 Cor. 5:19 could be periphrastic.
(3) θεὸς could be a predicate nominative rather than the subject of the verb ἦν.
Furnish prefers (2) and translates thus: "God, in Christ, was reconciling."
He sets his rendering off by commas "to make it clear that 'God-in-Christ' is not intended as an incarnational formula here [in 2 Cor. 5:19]. Nor does the phrase in Christ have the full eschatological meaning present in v. 17. Rather, as observed already by Chrysostom (NPNF, 1st Ser. XII:333), it is equivalent to through Christ in v. 18" (Furnish 318).
There is much more, so I encourage you to reference Furnish's treatment of 2 Cor 5:19ff.