"Go by yourself. I don't want to go!"
The exclamation point in the sentence indicates an imperative so I do not believe it is necessary to use 把 to soften it.
There is no grammatical command form in Mandarin. A declarative sentence beginning with 你 or 你们 can be understood as a command in context. Thus, 你去睡觉 is an imperative when said to a friend who is nodding off while watching TV. You can soften such a sentence by adding the final particle 吧 ba or by using words such as 应该 yīnggāi before the verb phrase. Negative imperatives often use 不要 bú yào or 别 bié, both meaning 'don't'.