If you're on the 8 p.m. flight out of Houston, you'll get to Stockholm around 5 p.m. That means you can collect your bag and fly back to London on the 9.20 p.m. flight on another booking for around £75 - so fly the entire ticket, collect your bag and check it back in, then have dinner in or near the airport before flying back to London.
If that seems like too much hassle, pay for a stopover and collect your bag in London, then fly to Stockholm for a day or a weekend in a few weeks or months' time and still save a fortune over just booking IAH-LHR.