The form is pretty clearly middle -- so far as I can judge, there are no passive
instances of this verb in the GNT. Note what BDAG says of the middle:
b. mid., in our lit. always w. impers. subj. (Diod. S. 13, 85, 2 the siege ‘went into effect’, ‘began’; Herm. Wr. 12, 11c τὰ ἀσώματα) τὰ παθήματα ἐνηργεῖτο ἐν τ. μέλεσιν the passions were at work in our members Ro 7:5 (the εἰς foll. introduces the goal; s. a above on Gal 2:8). ἡ παράκλησις ἡ ἐνεργουμένη ἐν ὑπομονῇ consolation that functions in (the act of) enduring 2 Cor 1:6. ὁ θάνατος ἐν ἡμῖν ἐνεργεῖται death is at work in us 4:12 (Lucian, Charon 2 ἐνεργεῖν τὰ τοῦ θανάτου ἔργα). Of God’s word 1 Th 2:13. δύναμις ἐνεργουμένη ἐν ἡμῖν the power that works in us Eph 3:20; cp. Col 1:29. πίστις δι᾿ ἀγάπης ἐνεργουμένη faith working (=expressing itself) through love Gal 5:6. τὸ μυστήριον ἐνεργεῖται τῆς ἀνομίας the secret force of lawlessness is at work = is in operation 2 Th 2:7. δέησις ἐνεργουμένη effective prayer Js 5:16. τὰ ἐνεργούμενα the forces at work 1 Cl 60:1. τὰ καθ᾿ ἕκαστα βλέποντες ἐνεργούμενα we see how one thing after the other works itself out = comes to pass B 1:7.—JRoss, ἐνεργεῖσθαι in the NT: Exp. 7th ser., 7, 1909, 75–77; JMayor, ibid. 191f; AGarvie, ET 55, ’43/44, p. 97. For the view that the passages in b are passive, not mid., s. the art. by Clark below, p. 98ff and ref. there.
I haven't see the article by Clark arguing for a passive sense referred to by Danker as KClark, The Mng. of ἐνεργέω and καταργέω in the NT: JBL 54, ’35, 93–101.
K. W. Clark's article was reprinted in his The Gentile Bias and Other Essays
(1980) 183-91, of which unfortunately Google apparently displays only the first few pages, not the part where he deals with the passive uses. His argument is that the agent of the verb is in the NT always some supernatural spiritual force (God or other), that this fits well in a 1st-century religious context, and it is not taken account of if you read the M-P forms as middle, as many do. Clark also refers to J Armitage Robinson, who in an Excursus in his Ephesians commentary takes the same line, at least for the Pauline instances.
"The passive interpretation being thus supported by the early Greek and Latin commentators, as well as by the constant usage in non-biblical Greek, we are naturally led to ask whether there is any necessity for a different explanation in the nine passages of the N.T. in which the word occurs."
Also: "It is to be observed that in actual meaning ἐνεργεῖν and ἐνεργεῖσθαι come nearly to the same thing. Only the passive serves to remind us that the operation is not self-originated. The powers 'work' indeed; but they 'are made to work'."http://archive.org/stream/MN41514ucmf_2#page/n253/mode/2up
On James 5.16, see also J. B. Mayor's 2 1/2 page discussion of the point. http://archive.org/stream/cu31924029294844#page/n487/mode/2up
The references given in the Bauer lexicon are not necessarily to be read with the glosses given there. E.g., Diod Sic 13.85.2
οὐ προσδεξαμένων δέ τῶν ἐν τῇ πόλει τούς λόγους, εὐθὺς τὰ τῆς πολιορκίας ἐνηργεῖτο is translated by Oldfather (Loeb ed.) "when the inhabitants of the city would not entertain these terms, the siege was begun at once". (More strictly, I suggest: was put into effect at once.)
This question was also discussed on the Better Bibles Blog http://betterbibles.com/2010/02/22/semantics-put-to-work-on-galatians-56/#comments