Penal Legion Troopers conversions

I have two Penal Legion Squads in my Warhammer 40000 Imperial Guard army. Both of them are made using the Catachan Guards plastic miniatures for the penal legionnaires and one Cadian imperial guard as the custodian. I decided to paint their "uniforms" orange as if they where took in a hurry from a prison and there wasn't any time or money to give them more than a lasgun.

In the unit description it is said that:

New legionnaires have their heads shaved and tattooed with their insignia. Explosive collars are clamped around their necks. The collars are a disciplinary device, primarily designed to discourage a prisoner from attempting to escape. The blast from one is directed inwards...

That gave me an idea, "shaving" the head of all the miniatures wasn't the one, it was to make some collars with green stuff. Nothing fancy, just a flatten putty sausage and a small square part to make the explosive part. Even if it isn't to obivius it gives them a little more aspect of penal legionnaires.

As you can see I haven't adapted the unit to my new colour scheme but it will only imply changing the bases, and the colour of the bandanas.