Specific namecoin address in merged mining
with p2pool at least for the coins are 'merged' mining you cannot reconfigure them to go to any other account except for the default account of that wallet.  However  you may be able to work around this in one of the following ways depending on your coding ability.
Monitor P2Pool logs and trigger script
Watch the p2pool logs and when a block is found trigger a script.
This can be achieved using swatch (linux tool for watching logs files) and looking for merged blocks that appear in /path/to/p2pool/data/bitcoin/log  (cant find the example merged block right now will edit later to include)  so in this instance what you would do is use this command:  swatch -t /path/to/p2pool/data/bitcoin/log  and create a ~/.swatchrc in your home directory with something like this:
watchfor /SHARE|BLOCK/
    exec echo &quot;P2Pool Event:\n\n$_\n&quot; | python ~/pyPushBullet/pushbullet_cmd.py 6xxxxxxxxxxxxxxxxxxxxxxxx60993c note xxxxxx&quot;P2Pool Notification&quot; &quot;$_&quot;

Im using push bullet to send notifications on share and block notifications.  however in your case you would want to craft a script to check the block itself for merged outputs.
Wallet Notify
Most Crypto Clients now let you configure an action for
  -blocknotify=&lt;cmd&gt;     Execute command when the best block changes (%s in cmd is replaced by block hash)
  -walletnotify=&lt;cmd&gt;    Execute command when a wallet transaction changes (%s in cmd is replaced by TxID)
  -alertnotify=&lt;cmd&gt;     Execute command when a relevant alert is received (%s in cmd is replaced by message)

Courtesy Off The Bitcoin Wiki
again in the same vein as the first optin you could  create a script that is triggered on wallet notify for the Nnamecoin wallet and move the coins from the default addreaa to you chosen address.