Let's see. Say you have a little over $3,000 worth of BTS, or 300,000 BTS. You use 200,000 BTS to short sell 58.53 BitSilver at the current price feed of 1,708.64 BTS/BitSilver. You use the other 100,000 BTS to buy up your short. This increases the supply from the current 288 BitSilver to 346.53 BitSilver (a 20% increase). The average expected yield metric reported on bitsharesblocks.com drops from the current 3.06% to 2.54%. By the way, while I was typing this the reported yield dropped from 3.41% (since the supply was 258 BitSilver) to 3.06% because of an additional 30 BitSilver added to the supply; it seems like people are taking your advice
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So, as more people try to get in on this free 3% p.a. yield, they will drive it down low enough that people won't bother. Of course they cannot actual claim the yield that they saw reported when they shorted. The only yield that matters is the one at the time they transfer their asset to themselves. They need to hold the asset for at least 24 hours before they can claim any yield at all. And even then the actual yield is the reported yield multiplied by the factor (0.2 * (1/365)^2 + 0.8 * (1/365)) = 0.00219. So the amount of free money received after 24 hours assuming the supply doesn't further increase (and no one else claims any of the 8.81 BitSilver currently in the yield pool by transfer their existing BitSilver to themselves) is 0.00219 * 0.03 * 58.53 BitSilver = 0.003845 BitSilver, which is currently worth approximately 6.57 BTS or 6.6 cents.
The important question to ask then is do you wait a few more days, d, to increase that factor f(d) = (0.2 * (d/365)^2 + 0.8*(d/365))? Or do you claim your yield as soon as you can before the reported yield drops as the supply increases? Determining the best strategy depends on making assumptions about what people will do in the future (increase/decrease in BitSilver supply, further market orders and transaction fees to increase BitSilver yield pool, BitSilver transfers that claim yield reducing the BitSilver yield pool). So, who knows. But what I wanted to point out is that the yield column in bitsharesblocks.com can be very misleading (especially for BitAssets with a small supply).