You actually need to get the LicenseAcquirer on the active media plugin, since the SMFPlayer class itself merely loads media plugins when playing content.
If all you want is to be able to set the override URI then you can use override the OnMediaPluginLoaded method in a sub-class of SMFPlayer:
protected override void OnMediaPluginLoaded()
ActiveMediaPlugin.LicenseAcquirer.LicenseServerUriOverride = new Uri("http://drm.example.com/");
If you don't want to sub-class SMFPlayer then the other option is to set it on your playlist item:
PlaylistItem item = new PlaylistItem();
item.LicenseAcquirer = new LicenseAcquirer
LicenseServerUriOverride = new Uri("http://drm.example.com")