As far as I know this is a firmware limitation, put there in part to avoid the added duty for video cameras, and in part to keep the sensor from getting too hot. About all you can do is work around it by timing your breaks.
There is some hacked firmware for some cameras, but I'm not sure there is for the D3100, and of course its a little dangerous to hack your firmware. Canon shooters have an advantage here, as the "magic lantern" firmware is more advanced and fairly reliable.
If you really want to pursue this, you might try Googling for Nikon firmware hacks, but it's a walk on the wild side.
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There is some hacked firmware for some cameras, but I'm not sure there is for the D3100, and of course its a little dangerous to hack your firmware. Canon shooters have an advantage here, as the "magic lantern" firmware is more advanced and fairly reliable.
If you really want to pursue this, you might try Googling for Nikon firmware hacks, but it's a walk on the wild side.