If the question is limited to if you can do it without sharepoint designer, I'd wager that you theoretically could do this with custom code within a CEWP, but you may have to carry this change throughout all subsites as the CEWP only really works on that specific page where it's located. Also, make sure to use Important! tags when possible.
As far as getting the code to make this change, do a search for Heather Solomon's CSS reference chart to find the correct CSS ID's and classes that you'd need to edit the global nav. I know the blog pages are a little different than regular team site/blank page masterpages, but overall I think you'll find those tags without too much issue.
While you're finishing up your solution, I think it's entirely worth the trouble of contacting your infrastructure team with a good business case (use this question/problem to help you present the idea,) to allow you to install SharePoint Designer, or to get administrative access to the masterpages. Not sure what the process would be for you to do that, but it will pretty much sell itself from the minute you can get in there and start tweaking things. Not to mention, it's freeware.