Check out http://www.the12volt.com
. Find their calculators page and search for the series/parallel calculator.
What is the amp rated at? Do you care about stereo or fade? If you do it probably won't be possible. The speakers will have to be wired parallel to each other then connected to the amp, which will keep them at 4 ohms.
EDIT: Is the amp bridgeable? Just realized it wasn't to keep it ohm stable. The amp will have to be bridgeable in order for it to work. Speakers will still need to be wired in parallel.
To bridge a 2 channel amp:
You will see the speaker out puts in some form of ++-- or +-+-
The bridgeable outputs are usually labeled, or each channel is labeled. Basically use the positive for one channel and use the negative from the other channel. So if it the if the outputs look something like:
CH A (+ -) CH B (+ -)
You would use CH A (+) and CH B (-)