XiBO RSS feed expiration

Not sure if this is possible, but we use XiBO purely for displaying message (no flash content, just scrolling and static messages). I have normal and urgent messages in xml files that XiBO pulls from.
Is there a way within XiBO to set when items expire in the RSS feed? For example if we have the two following items:

<item>
<title>Open Day</title>
<description>Open Day letter on Parent Portal. Everyone please bring back reply slip ASAP. Lots of help needed from all girls!
</description>
</item>

<item>
<title>German Language Trip</title>
<description>The final reply slip / deposit deadline for the German Language trip is Monday 12th September.
</description>
</item>

Now obviously the first one can stay on a while, but the second needs to be removed by the 13th Sept. I was wondering if there was a way I could add sort of an <expire> tag and put a date in, and when it gets to that date, the notice is removed. At the moment I have to go in daily and read the messages to see which are out of date.
If not it's not a worry, just a thought. I suppose I could just add an <expire> tag myself that is hidden to the feed so when i view the xml i can see which are to be deleted

Really you want to be automatically generating the rss from something that does support such things

Any recommendations?
I still need the two xml files as the feeds as they are used elsewhere, but if you can recommend something to use that can do this sort of stuff please let me know

I dont think Xibo can do this as the schedules it handles are per layout. Meaning you could specifiy when the layout would expire but not the content inside it. I agree with mavhc that you should probably be looking at the RSS feed rather than Xibo, but dont know how you would do that sorry.