Unfortunately, this is the only way to do what you want to do in SQL Data Compare.
However, we have an alternative tool called SQL Data Generator which is specifically designed to aid with the insertion of test data into development databases. Using this tool you can specify your test database in the project and specify the number of rows to generate (in Tools > Application Options > Generation tab and Specify number of rows).
At this point you will need to make a decision. Either generate 'random' nonsense data into the tables, or specify your source tables (containing the data). Unfortunately, the latter will need to be done for each table individually . But the former, will be much quicker to set up (as it uses 'random' data generators as standard).
http://www.red-gate.com/supportcenter/c ... s_or_views
But if you have any questions then please let me know.