preload css text file

I know how to preload an external file using LoadVars. Now I want to combine it with loading a text file containing html tags. For example: I'm loading a text file which contains:

<img src="mybigimage.jpg" />

And let's suppose this jpg file is large, like 3 mb. Now when I would load it directly through LoadVars I could use getBytesLoaded/getBytesTotal and I would see the percentage in a textfile go from 0 to 100%.

But when using it on a textfile containing just the img tag (I'm using css in flash), the text file would load almost instantly. It wouldn't preload the jpg but the txt file instead.

Is there a way to show the loading of the file mentioned in the img tag?