The following MBean works for me:

package test;

public interface BouncyCastleMBean
{
 public void start() throws Exception;
 public void stop() throws Exception;
}


package test;

import java.security.Security;
import javax.crypto.Cipher;
import org.bouncycastle.jce.provider.BouncyCastleProvider;

public class BouncyCastle
 implements BouncyCastleMBean
{
 public void start() throws Exception
 {
 BouncyCastleProvider bcp = new BouncyCastleProvider();
 Security.addProvider(bcp);
 Cipher c = Cipher.getInstance("RSA", "BC");
 System.out.println("Created RSA cipher: "+c+", provider:"+c.getProvider());
 }
 public void stop() throws Exception
 {
 BouncyCastleProvider bcp = new BouncyCastleProvider();
 Security.removeProvider(bcp.getName());
 }
}

[starksm@banshee crypto-121]$ jar -tf output/bouncycastle.sar
META-INF/MANIFEST.MF
META-INF/jboss-service.xml
test/BouncyCastle.class test/BouncyCastleMBean.class
bcprov-jdk14-121.jar