It would also help to know a little about the radio station. For example if teens are important to you; they'll be back in school soon. You could do some sort of "school spirit/challenge" contest. Like a Penny Jam. School that collects the most penny's wins a concert at their school from an artist.
No teens?
If your station has a text message platform thru someone like Hip Cricket or MSnap you can work with them to set up an easy way for people to donate.
They could simply text the word "donate" to whatever your station's short code is to donate a pre-determined amount. Say $4.99. Doesn't sound like alot but do the math:
If you're in a small market and your cume is only 90,000 and 1% of your cume sends a text message for this promotion that adds up quickly.
This kind of campaign would target listeners who want to donate but are too busy to visit the drop off location(s). If your sales team is good, they could sell this to a client and all listeners that donate could receive a coupon via text-message from the client.
Or you could have a jock live on a billboard. But if you do something like that he/she needs to be up there all the time. Nothing would look more silly than if people showed up and he/she was in some RV next to the billboard having a quarter pounder with cheese.
Or you could do a radiothon with your morning show on the air for two straight days broadcasting from center court at a mall. Set up the phone banks in the mall with them. Interview people from the charity, and people the charity has helped (real emotional tear jerker kinda things).
I'm tapped out. If none of those helps, I suggest gathering up some staff members (do not include any managers other than Promotions) and drinking some Grey Goose until you're good and buzzed then start kicking around ideas. The reason no managers? They would give you a thousand bullshit excuses why they couldn’t do any of the ideas that come up in the meeting.
One of the problems with radio these days? Reaction time. The waiting. The plotting. The meetings. Instead of just saying “F it, let’s do it.”
If done creatively, your fundraiser would be another thing that strengthens the bond between you, your audience & your community at large. And makes your station memorable. It's something radio can do that plays to our strengths.
What can we do that an iPod can never do? Evoke emotion.
Good luck.