Why is the particle を used without a verb in the following context?


First of all, this question shares the same context with [another Q&A asking
for the meaning of
手{て}かがり](https://japanese.stackexchange.com/q/100375/32952).

What follows is an excerpt from N2新完全マスター, in particular the section 問題紹介
where they are explained the different exercises that appear in the N2
Japanese Language Proficiency Test:

[![enter image description
here](https://i.stack.imgur.com/aBxMS.png)](https://i.stack.imgur.com/aBxMS.png)

I have trouble understanding the following sentence:

> 【例題3】では「〜について」「〜に対する」という文法形式 **を** 手がかり **に** 、その前後にどんな言葉がくるかを考えます。

Where is the verb corresponding to the highlighted particles を and に? It sure
can't be 考えます because it takes another を.

Finishing the relative clause adverbially with 手がかりに feels incomplete and
abrupt. I found [this related
Q&A](https://japanese.stackexchange.com/q/20854/32952) where they explain that
sometimes the verb is omitted in the construction AをBに, but this sentence
doesn't seem to fit the typical examples with body parts and such listed in
the [accepted answer](https://japanese.stackexchange.com/q/20854/32952).

Is して implied here, as explained in the [alternative
answer](https://japanese.stackexchange.com/a/20855/32952) of the same Q&A, or
what is going on?

> 【例題3】では「〜について」「〜に対する」という文法形式 **を** 手がかりに[ **して** ]、その前後にどんな言葉がくるかを考えます。In
> the example 3, [ **make a hint of** ] the grammar forms について and に対する, and
> think of what word comes before and after them.

