Sub-prime second mortgage loans are the way to go if you have a poor credit history. Come clean with your lender, and ask them if you qualify for a sub-prime loan. If they don't offer them, they might be able to steer you to an institution that does.
When shopping for a second mortgage loan, don't just take the first good interest rate you see. Get quotes from at least one bank, one credit union, and one dedicated mortgage lender, and keep a close eye on the various fees charged, because they can add substantially to the cost.