Is there a way to forestall vanilla bean marrow falling to bottom of crème?
Personally the only way I've ever achieved a good suspension of vanilla in my Brûlée's is by cooking the custard over a bain-marie until thick and... custard like. Once it's nice and thick I'll then pour it into my molds and then bake them for 10-15 min at around 110°c just to finish off. Be very careful not to over cook them the last thing you want, after all that stirring over the bain-marie, is curdled eggs. 

The extra thickness of your custard helps stop the vanilla seeds sinking to the bottom. However, you will still get a little sink-age.

The trick for Pannacotta, is to stir them as they begin to set. Or to whip them after they have set and then stick them back in their molds and chill again. This also helps make your Pannacotta lighter and aerated.