In a loosely packed bed of ...

In a loosely packed bed of uniform sand grains, you have between 40 and 45 volume percent of pores. Probably you can increase to 50% or a bit more porosity in a further expanded bed, still sufficiently consolidated, by slightly touching sand grains, that are properly fused when heated to 1650 °C. If this is worth the trouble, I guess you cannot use sugar grains, but must use molten/syrup sugar as otherwise, the sugar grains will melt at 160 °C and your expanded bed may collapse?

Suppose, you use sugar, then why not add and mix with sand until total volume starts increasing. At that point, the added volume of sugar is the pore volume of your (loosely) packed quartz sand. Any extra added sugar volume is then likely the extra pore volume that will be generated.

I guess, upon heating and pyrolizingthe sugar to char around 200 °C, foaming occurs, and the bed will not collapse but needs confinement to avoid expansion.

I imagine, the foam remains stable while you fuse the sand and then burns away after you allow access of oxygen.  

I wonder if magnesium oxide is an alternative for sugar. It might be more inert well beyond the fusing temperature of quartz, having a melting point of 2800 °C and it is more soluble in acid than quartz, allowing removal by dissolution.