How to add comment in apache httpd.conf not as a complete line?

The documentation states that it is not possible:

... Lines that begin with the hash character "#" are considered comments, and are ignored. Comments may not be included on the same line as a configuration directive ...

I believe only # is parsed as there is no real need for it. But if you really need you can use IfDefine block, which will be ignored unless a matching variable has a definition.

<IfDefine myexisterenceIsForJustAComment>...</IfDefine>

Look at discussion at : https://bugzilla.redhat.com/show_bug.cgi?id=1349546

Not sure if these are supported in latest versions (< httpd-2.2.15-53) but you can try below which was supported in earlier versions. You may be in luck if you are on older version.

In earlier/older versions of Apache, I remember it was okay to include a comment at the end of a line (wrapped in double quotation marks), like so:

<Limit GET >    Order Allow,Deny    Allow from all    Deny from xxx.xxx.xxx "# I am in inline comment"</Limit>

Apache interprets its conf files line by line. And it considers a line starting with # as a blank line (or line break) and skips the line.Also it doesn't have a symbol to indicate comments because conf files have many special symbols, which might let them to disable middle-line comment.