I recently picked up the Tapco Intrafuse T6 rubber butt-pad, from an ebay vendor for around $12,delivered. I've been telling all my freinds about what an excellent product this thing is, and how these things should come stock on all these little plastic retractable stocks.
The go on without a lot of difficulty, but stay in place very well.
I think it only provides another 1/2" or so of LOP, but with these little stocks, every bit helps.
What i most like about it is that it increases the overall surface area of that hard-edged plastic buttplate, and smooths all the edges out, particularly that bottom corner of the stock that tends to dig into your shoulder.
Again, IMO these are an excellent product that really improve the comfort and ergos, and you just can't go wrong at $12,delivered.