How to tack fuse glass frit and keep pores in glass
Try using the glass beads without grinding them to a powder first. The spaces between the spheres would then give you the pores you are looking for. Alternately you could mix in a material with a higher melting point to create gaps, being sure you do not fire above what is needed to fuse the lime glass. The risk here is different expansion rates between the materials may cause it to fracture and you may not be able to get all of the resist material out of the finished piece.  

Soda lime glass has a relatively low melting point (505°C), lower than borosilicate glass. You could tack them together using a torch instead of a annealer/kiln. Then you would have direct visual control over the amount of fusing and/or melt. If that is not possible then target the kiln to just touch their melting point and immediately start to cool.