We've been using plugged vias in SMT pads for years.  Our design calls for a 
.020" via in the solder pad.  The back side of the multilayer board is capped 
with a polyimide layer to prevent the vias on the back from shorting to a 
restraining core which the boards are bonded to after assembly.  During the 
cap layer bonding process, the vias are filled with a polyimide resin which 
flows up to the top of the vias.  We then require the fab house to over-plate 
the pads, including the polyimide resin-filled holes with copper, then solder 
coated.  The end result is a via in a pad that is, for the most part, 
undetectable.

This design worked great over the years, although the art of performing this 
process seems to have been lost since it's now difficult to find a fab house 
who can supply a quality product consistently (military qualified, low 
volumes). 

If anyone knows of a board vendor who can build such a board, please let me 
know.

Thanks,

Jim Marsico
(516) 595-5879
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