Put the following in the init line of the chopper and sync to PCS:

this setvariable ["CS_TYPE","TRANSPORT"];
this setvariable ["CS_CALLSIGN","Callsign of unit"]; //<- optional
this setVariable ["CS_SLINGLOADING", false];

And about the clutter, good question!

Thanks @Friznit!
@DLEGION and to whom it may concern! If you use the "Player Combat Support" you can use this after the next update:

this setVariable ["CS_SLINGLOADING", false]; //disables sling loading on transport helis

For more information visit: http://alivemod.com/wiki/index.php/Combat_Support

Same problem here and I also use "Player Combat Support".

Couldn't one write some thing like this, if one knew the name of the variable for slingloading?

this setvariable ["CS_TYPE","TRANSPORT"];
this setvariable ["CS_CALLSIGN","MUMAKIL"];
this setvariable ["CS_SLINGLOAD","NOPE"];