I had success about 6 monts ago with an installment account. It was an auto lease through GMAC. I had one 30 day late and wrote them a letter, pointing out my payment history since then and that I had opened two more accounts with them since then.
They never responded back to my letter but, as I kept my CR's on TC the tradeline dropped off in about 4 weeks.
Good Luck
FICO scores on November 17, 2014 (prior to applying for and being approved my mortgage)
EX=738
EQ=735
TU=754
FICO scores on March 4, 2015 after being approved for mortgage and buying the home, the mortgage isn't yet reporting.
EX- 689 EQ- 739 TU- 739