In short, when this has been brought up on other StackExchange sites the answer has always been the same. If you need to leave a comment on a question and can't - move to another question. Comments are really second class citizens in the network. If it's a pressing enough detail then there is a high chance someone else will ask that question.
However, there is a way to Constructively comment on a question. For instance if a question is extremely too vague to even provide an estimated answer - just move on. Though if you can provide a ballpark answer you can try the follow.
Can you please provide X, Y, Z details in your original question?
You can also try the following:
This way you're providing feedback to the user, who can either comment on your answer, edit their question, or ignore it completely. Lower rep commenting rules work as follows: If you're the author of the question you can comment on any answer. If you're the author of an answer you can comment on your answer. Thereby allowing you to address each accordingly. It's designed to strongly ingrain the idea that Comments aren't required and should be used sparingly.
This is best discussed and demonstrated on Joel Spolsky's Blog post: Stack Overflow Launches
Note: This blog post was written before the comment system existed on the StackExchange network However, for low rep users the same concept applies.
While we encourage users to cut the extended discussion to a minimum it's often necessary to gather the minimum data to give that accurate, awesome, authoritative answer.
Along with helping to focus users on how to properly use the system - it's design (whether by design, or accidental) encourages users to participate by rewarding them for gathering reputation and providing a sense of entitlement. Now you can comment, create new tags, edit other peoples posts, vote to close, 10k user tools. If you work to gain 2k reputation then abuse the editing power your account will have actions taken against it and you'll have to work twice as hard on a new account to gain that level of destruction again. So just as much of an encouragement to participate it's also a deterrent once you gain that power.
It can be frustrating at times - being a new user and having such a low restriction - but the system is truly designed around one purpose. Questions & Answers.