这不能说是“虚拟语气的省略形式”。这只能说是省略从句跟主句重复的部分。

He opened his lips as if to say something. = He opened his lips as if he wanted to say something.

方式状语从句中，省略“主语 + be” 的用法也十分常见：

She talked to the stranger as if (she were) absent-minded. 她和陌生人谈话时似乎心不在焉。

He opened the drawer，as if (he was) in search of something important. 他打开抽屉仿佛要找什么重要的东西。

She stood at the gate as if (she was) waiting for someone. 她站在门口好像在等人。

The teacher shouted at the boy as if (he was) angry. 老师朝孩子大喊大叫好似很生气。