(1) Assuming a slave's form is a fitting expression of Christ's humility. Nevertheless, a fatal objection to Robert Bowman's view of the participial phrase in Phil. 2:7 is that his explanation makes KENOW refer to an act of addition--not to an act of subtraction. Yet lexical evidence for this use of KENOW is sadly lacking. One may consult BDAG, Louw-Nida, LSJ or Moulton-Milligan's and he or she will likely not find one instance where KENOW describes an act of addition. Neither in Holy Writ nor in extra-biblical literature does one find an instance of this Greek verb employed in the manner that Bowman suggests.
(2) The aorist participle LABWN, if translated woodenly, would be rendered "having taken" or "received" the form of a servant. It would thus have reference to an action that is antecedent to the main verb. But there are also times when the aorist participle has ingressive force.
At one time, I favored the antecedent view for the participle LABWN in Phil. 2:7. After talking with a friend and studying Stanley Porter's Idioms, however, I must concede that LABWN may be referring to consequent action or another possibility is subsequent action. At any rate, it is by no means certain that LABWN is a participle of means. While categorizing Phil. 2:7 as an example of the instrumental participle (i.e., participle of means), Brooks and Winbery admit that LABWN and GENOMENOS "may indicate manner rather than means" (Syntax of NT Greek, 150). To be fair, they also say that there's little difference between a participle of manner and one of means. However, the disparity between the two is significant enough to demonstrate that Bowman may only be appealing to a grammatical principle that suits his theology. For a brief (but lucid) explanation of the difference between means and manner, see Richard A. Young's Intermediate NT Greek, p. 154.
Bowman also writes:
"but there need not be an argument here at all. In Trinitarian theology it is true to say that Christ actively took this action [i.e., the kenosis], and it is also true to say that the Father sent Christ and gave him his human nature (including his body). It is not either/or; it is both/and."
Maybe acording to Trinitarian theology, Christ actively "incarnated himself." But my concern is whether the Bible makes this claim. So far, you've offered one controversial text to support your theological view and not much else. And the lexicons I've checked so far all agree that KENOW does not refer to an act of addition. Furthermore, grammarians who are interested in scholarship (rather than propping up Trinitarian notions), also concede that the context of Phil. 2:7 possibly does not really favor LABWN being a participle of means. Construing it thus is only a convenient way to seemingly buttress your view of the Incarnation and God's putative triunity.