The single-domain license is intended to discourage piracy and to help keep my support responsibility within manageable limits. I have no objection to users installing simpleContact Pro multiple times on the same website - in fact, until I implement multiple forms in version 3.0 it is my recommended solution:
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1) Upload a new copy of simpleContact Pro
Upload a new sc_admin folder and the form files that you need (with their names changed to prevent over-writing your first copies).
2) Edit config.php
Many hosts will charge you for additional databases, so I recommend that you install multiple copies of 'Pro into the same database.
Open config.php in your new sc_admin folder.
Change the $table_prefix_pro setting to be something else (e.g. "scpro2_") - this will make it install tables with different names to your existing installation, preventing conficts.
3) Edit your form files
Open your new form files and change the file links at the top to point to your newly uploaded sc_admin folder, by whatever name you have given it.
The only thing remaining to do is edit the action value on the form tag so that it posts to the file's new name (e.g. "contact2.php").
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For example, if your website's file system looks like this:
contact.php (paths inside the file linked to sc_admin)
sc_admin (folder)
|_ config.php (with default table prefix)
... your second install could look like this ...
contact2.php (form with its name changed - paths inside the file linked to sc_admin2)
sc_admin2 (folder - a duplicate of sc_admin, with its name changed)
|_ config.php (with edited table prefix e.g. "scpro2_")
You now have two self-contained installs, which use the same database (but not the same tables). You can repeat this process as often as you need for your website.
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simpleContact Lite
Users are of course, free to install Lite where ever they wish. The same method works in principle, with small differences:
Open sc_config.php
Change the $table_prefix setting to be something else (e.g. "sc2_").