You should be able to edit and save your Blogger template file.
- Open template file: on your dashboard, go to Layout | Edit HTML to open the template file.
- Create a backup: click Download Full Template to download a backup copy before editing your template file (just in case).
- Check Expand Widget Templates to see the full template.
- Search for the following lines of code within the template (you will insert the AddThis code, i.e. the hack, right above these lines):
</div> <div class='post-footer-line post-footer-line-2'>
- You'll probably want to replace JOHNDOE (line 5) with your AddThis username. If you don't have an account, you can register to AddThis for free.
- That's it! Just click Save Template and watch the result.
Of course, you can change the float:right; statement (line 8) to float:center; or float:left; to align the button to the center or to the left, respectively.