What about just putting a large-ish UPS[1] on the generator output? Get a higher-end UPS that will tell you the state of charge, and run the generator as needed.

eg: http://canadiantire.com/browse/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524443289558&FOLDER%3C%3Efolder_id=1408474396673606&bmUID=1182542683289

Alex

[1]Uninterruptible Power Supply: Typically used by people who have experienced the sinking sensation of watching a 10-page document disappear when the computer abruptly dies in a power failure, and who are seeking to avoid feeling that sensation again.