Is there an implied verb after に, or not? Is this sentence more along the lines of the situation when you have two verbs connected with the ～て form, or is it more along the lines of "兄さんをエサに" being an element of the verb 引っ張り出す in the same way that ホムンクルスを is?
Could you replace に with として here? If so, how would it compare with the sentence using に? If not, why not?
I know I asked a lot of questions; just address whichever ones make the most sense.