J. Ross Wagner is an associate professor of NT at Princeton Theological Seminary. He did his Ph.D. at Duke under the supervision of Richard B. Hays. His dissertation was published by Brill as part of Supplements to Novum Testamentum in 2002 under the title Heralds of the Good News: Isaiah and Paul "In Concert" in the Letter to the Romans. It's an excellent study of Paul's quotations of and allusions to Isaiah in Romans 9-11, utilizing Hays's theory of intertextuality set forth in his groundbreaking and influential work Echoes of Scriptures in the Letters of Paul.
Here is a good summary of Wagner's thesis in his own words:
Paul's citations and allusions to Isaiah are not plunder from random raids on Israel's sacred texts. Rather, they are the products of sustained and careful attention to the rhythms and cadences of individual passages as well as to larger themes and motifs that run throughout the prophet's oracles. Paul finds in Isaiah a fellow preacher of the gospel, the message that reveals God's righteousness for all who believe ... Through adopting as his own the stories Isaiah and his fellow scriptural witnesses tell about God's unquenchable love for his people, Paul finds assurance that God will be faithful to redeem and restore his covenant people Israel, so that Jew and Gentile together can sing the glories of God's name (p. 356).
The above quote aptly summarizes two of Wagner's main points: (1) that Paul was not a proof-texter (as Christopher Stanley claims) but one who carefully studied and interpreted Isaiah as a whole, and (2) that Paul relied on Isaiah's prophecies because they supported his belief that "all Israel shall be saved" in accordance with God's covenant faithfulness to his people (= "the righteousness of God" according to Wagner).
I like the first argument but not the second. I'll get to the second point in a moment, but a word about the first argument first. It seems as if Wagner's dissertation is in some ways one large argument against Christopher Stanley's view that Paul was a proof-texter who quoted verses of Scripture out of context to score rhetorical points with a largely illiterate Gentile audience who knew next to nothing about the Scriptures. One of Stanley's articles is titled, "'Pearls Before Swine': Did Paul's Audiences Understand His Biblical Quotations?" (NovT 41 : 124-44), to which his answer is "basically, no." (See also Stanley's Arguing With Scripture: The Rhetoric of Quotations in the Letters of Paul, although this came out two years after Wagner's dissertation was published.)
Against Stanley, Wagner does a good job showing that, in the case of Paul's use of Isaiah in Romans 9-11, at least, there are very good reasons to think that Paul was quite familiar with the larger context of the passages he quoted, even to making unmarked intertextual allusions to broader themes. A good example of this is Paul's use of the Suffering Servant material. He quotes Isa 52:15 in Rom 15:21, as well as the very next verse, Isa 53:1, in Rom 10:16. He also alludes to Isa 53:5, 11-12 in Rom 4:25--5:1 (there are four verbal parallels in Greek -- look it up in the LXX and see if you can find them!).
Wagner (p. 335 n. 107) cites Hays favorably at this point:
[Paul] hints and whispers all around Isaiah 53 but never mentions the prophetic typology that would supremely integrate his interpretation of Christ and Israel. The result is a compelling example of metalepsis: Paul's transumptive silence cries out for the reader to complete the trope (Echoes, p. 63).
Many other examples can be cited to support the notion that Paul had immersed himself deeply in Isaiah and knew it backwards and forwards. Wagner suggests that he may have even committed large parts of it to memory.