There is no configuration option to change what actions the "Home" button does on the toolbar for customers. You could potentially change the underlying Perl code that generates the toolbar but I do not know how to make the button always go back to the customers default workspace. In addition, any code changes are not supported by Tech Support and will get overwritten upon upgrading.
With that said, if you'd like to poke around on your test server, you can edit the GetToolbarRegular.pl file in FootPrints\cgi\SUBS. Find the following line:
You can read through the block of code, making note of:
# for customers already logged in, home will most likely default to "my requests", unless not allowed to submit
$url .= "&CUSTOMER_WELCOME_PAGE=1";
Let me know if that gets you started in the right direction.