Is there a way to lessen the unpleasant smell of steamed broccoli?
Cook it less, if you can. The more you cook it, the more you get that smell. Perhaps you are just more sensitive to it than most; I don't generally notice it until it's overcooked by my standards.

Along with this, cook it as fast as you can. The flavor you don't like is produced by enzymes converting precursor molecules into those with the flavor. From On Food and Cooking:


  Heating cabbages and their friends has two different effects. Initially the temperature rise...speeds the enzyme activity and flavor generation, with maximum activity around 140F/60C. The enzymes stop working altogether somewhere short of the boiling point. If the enzymes are quickly inactivated by plunging the vegetables into abundant boiling water, then many of the flavor precursor molecules will be left intact. ... If the cooking period is prolonged, then the constant heat gradually transforms the flavor molecules. Eventually the sulfur compounds end up forming trisulfides, which accumulate and are mainly responsible for the strong and lingering smell of overcooked cabbage.


So as suggested by others, boiling instead of steaming to reduce cooking time helps. So does cooling quickly, with cold or ice water. Boiling in excess water will also leach some out, but you might also lose flavor you like.

A couple other thoughts, also from On Food and Cooking. Cabbage family vegetables grown in the summer, and under drought stress, produce more of the flavor precursors, and those grown in the autumn and winter with less light and more water have less. They're also more concentrated in the core of the vegetables. And for cabbage, you can remove a lot of them by chopping and soaking in cold water; conceivably the same could work for broccoli, but again perhaps at the cost of desirable flavor.