That kind of manual change is a bit scary I have to admit, wouldn't using the host name from PHP as a discrimination to identify the target node work?

I'm definitely over-simplifying but something like:

```php
//config
$wgMoxiTestNode = 'ap-s4';

//code
if ($curr_host = $wgMoxiTestNode){
//replace MemcacheClient class
}
```