At Bible study earlier tonight (we're going through 2 Peter) we came across 2Pe 2.15-16:

Forsaking the right way, they have gone astray. They have followed the way of Balaam, the son of Beor, who loved gain from wrongdoing, but was rebuked for his own transgression; a speechless donkey spoke with human voice and restrained the prophet’s madness. (2Pe 2:15-16)

And here's the Greek. Note the words in bold between the two:

καταλείποντες εὐθεῖαν ὁδὸν ἐπλανήθησαν, ἐξακολουθήσαντες τῇ ὁδῷ τοῦ Βαλαὰμ τοῦ Βοσόρ, ὃς μισθὸν ἀδικίας ἠγάπησεν ἔλεγξιν δὲ ἔσχεν ἰδίας παρανομίας· ὑποζύγιον ἄφωνον ἐν ἀνθρώπου φωνῇ φθεγξάμενον ἐκώλυσεν τὴν τοῦ προφήτου παραφρονίαν. (2Pe 2:15-16)

This is in the context of a rather severe denunciation of false teachers. Rather than go the right way (the way modelled by angels in v. 11) these false teachers instead think lightly of judgement and embrace blasphemy. Like Balaam (a prophet for hire saying whatever he wanted [or whatever his benefactor desired] who was set straight by a dumb donkey), they have chosen the wrong way.

When I read this, I couldn't help but think of the Didache:

There are two ways, one of life and one of death, and there is a great difference between the two ways. (Did 1.1)

And here's the Greek:

Ὁδοί δύο εἰσί, μία τῆς ζωῆς καὶ μία τοῦ θανάθου, διαφορὰ δὲ πολλὴ μεταξὺ τῶν δύο ὁδῶν.  (Did 1.1)

This, of course, is similar to the Epistle of Barnabas:

But let us pass on to another lesson and teaching. There are two ways of teaching and of power, the one of light and the other of darkness; and there is a great difference between the two ways. For on the one are stationed the light giving angels of God, on the other the angels of Satan. And the one is the Lord from all eternity and unto all eternity, whereas the other is Lord of the season of iniquity that now is. (EpBarn 18.1-2)

And, again, the Greek:

Ταῦτα μὲν οὕτως· μεταβῶμεν δὲ καὶ ἐπὶ ἑτέραν γνῶσιν καὶ διδαχήν. Ὁδοὶ δύο εἰσὶν διδαχῆς καὶ ἐξουσίας, ἥ τε τοῦ φωτὸς καὶ ἡ τοῦ σκότους· διαφορὰ δὲ πολλὴ τῶν δύο ὁδῶν. Ἐφ ̓ ἧς μὲν γάρ εἰσιν τεταγμένοι φωταγωγοὶ ἄγγελοι τοῦ θεοῦ, ἐφ ̓ ἧς δὲ ἄγγελοι τοῦ σατανᾶ. Καὶ ὁ μέν ἐστιν κύριος ἀπ ̓ αἰώνων καὶ εἰς τοὺς αἰῶνας, ὁ δὲ ἄρχων καιροῦ τοῦ νῦν τῆς ἀνομίας. (EpBarn 18.1-2)

To be clear: I think Second Peter is earlier than both the Didache and the Epistle of Barnabas. And it seems plain enough that the idea of opposites (here in the form of two "ways") is used frequently in all sorts of literature. For example, we know the gospel and first epistle of John both use the opposition of light and dark in a similar way to contrast alternates. Even the quote from Epistle of Barnabas above uses the light/dark metaphor to reiterate the difference between the two ways.

Is this a not-so-direct mention of the "two ways" in 2 Peter? The one way is right/straight/proper (εὐθεῖαν) and the other way is associated with Balaam and is astray (ἐπλανήθησαν) from the right way.

Whether or not 2Pe 2.15-16 is a reference to "two ways" imagery similar to that of the Didache and the Epistle of Barnabas, the idea that there are two ways, and that one way is right and proper and the other way is not seems fairly clear, at least to me as I read this (admittedly late).