Can;t that get you banned? Google is pretty adept at ferreting these things out.
Info from the AdWords Help Center on the topic of Multiple accounts:
Can I have multiple AdWords accounts?
[adwords.google.com...]
If in doubt as to whether the info there applies to your particular situation, it's probably best to consult with AdWords support before opening another account. Let them know what you are hoping to achieve, and ask what your options are.
Before even considering a second account as a means to increase your keyword count, however, I'd advise clearing your account of what you consider to be your least valuable or least important keywords (what you might call the deadwood), and then check with support to see if your limit might be raised - assuming you still need more once the low value keywords are gone.
AWA