You can have a button, but not a drop down menu...
Ok, go here ->
https://www.paypal.com/cgi-bin/webscr?cmd=_donate-intro-outside
Create your own button, generate it.
then an HTML tab will open up, and an EMAIL tab will also.
get the image links from the HTML and paste 'em in image tags. Then click the email tab, and copy that link... now put that link in a URL tag around the image tags and your done.