There is a tiny app called pastebinit that posts any info you provide to various pastebin services, such as paste.ubuntu.com, pastebin.com, etc.

However the man page does not specify how to set the defaults.

You can create ~/.pastebinit.xml file in your directory with the content similar to the following:

<pastebinit>
    <pastebin>http://paste.ubuntu.com</pastebin>
    <author>author</author>
    <jabberid>author@example.net</jabberid>
    <format>text</format>
</pastebinit>

See the answer on Launchpad.