We have found that the primary way to deal with this problem is HDMI cable selection. There is a huge variation in HDMI cable construction and quality and we have seen differences up to 20dB between radiated emissions tests depending only on the cable choice. There is no correlation between cable cost and quality/performance in my experience. I recommend using a triple-shielded cable and keeping the length to a minimum of course. There are also commercially available cables with ferrite cores built in at both ends that work well. If you have a closed system this type of cable would be a cheap and effective solution to most problems. Since we are designing a receiver based product most of our problems are the sourced from the HDMI transmitter that we use to test the system. With careful cable selection we can pass commercial FCC and CISPR Class B emissions limits.
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