yes, you could use a key stored in the database.
on your map page, the following code sets the api key being used:
<script type="text/javascript" src="http://maps.google.com/maps?file=api&v=2&key=<api key here>">/*wagmp*/</script>
you could add arecordset to the page to pull the api key from a database and use the value from the database:
<script type="text/javascript" src="http://maps.google.com/maps?file=api&v=2&key=<?php echo($row_recordsetName['ColumnName']); ?>">/*wagmp*/</script>