It has been noted that in LDS scripture there is sometimes made a distinction between Isaiah and Esaias as well as Elijah and Elias. "Elias" is consistently used as a title for someone who prepares the way for the coming of the Lord. Thus in the Bible John is referred to as "Elias." (See http://en.fairmormon.org/Elias_and_Elijah_at_the_Kirtland_Temple for more information on the use of Elias in the Church)
As far as Isaiah goes, the Hebrew name Yesha'yah[u] (transliterated as Isaiah) appears in the Bible on many occasions, but is used to denote different individuals other than the prophet who authored the Book of Isaiah. These names are rendered Esaias in the Greek Septuagint, and are rendered Isaiah, Jesiah and Jesaiah in the KJV and many other translations of the Old Testament. In the passages in LDS scripture (apart from the Bible) that refer to Esaiah, it is possible that Joseph Smith was using a different transliteration of the Semitic name to differentiate one Isaiah from another. Indeed, we have many New Testament parallels in translation literature, such as the Jude/Judas variant in the New Testament where the translators chose to use "Jude" in an attempt to distinguish from "Judas" who betrayed Jesus.
In the nineteenth century, "Elias" was used rather generically to denote a forerunner. Alexander Campbell, in Delusions used it in the same fashion as did Joseph Smith:
The Jews gave up their business and attended to him. He obtained one Nathan in Jerusalem to pass for his Elias, or forerunner. (www.lds-mormon.com/campbell.shtml)
In many places, the Lord says that the revelations received by Joseph Smith were put into his own language according to his own understanding.(See D&C 67:5). It is likely, therefore, that he would have used "Elias" as a name-title for forerunners.
The Elias in D&C 27 seems to be Noah, who Joseph Smith identified with the angel Gabriel, and could well be the same as the one in D&C 110 (in section 27, Elias [clearly Gabriel/Noah from the context] was promised to bestow keys of authority. This may have been fulfilled as recorded in D&C 110).
I hope this adds some helpful information to this somewhat difficult question.