Auxilia with slings

Now, in the Infamy, Infamy rules, the only slingers that are listed for the Early Imperial Romans are "Tribal Slingers", but because some of us were discussing Roman slingers on the Infamy Facebook page, I cobbled a group of eight together. I used arms with swords from my Victrix Auxilia sprues, cut the hands off and glued on slinger hands from the Gripping Beast "Dark Age Warriors" set, and here they are;

I think that slingers can be justified because the rules state that Roman Auxilia are equipped with Mixed Weapons, which are described as "The weapons of most Foot and Mounted Warriors and include swords, spears and javelins". I am thinking that "include" doesn't preclude the use of other weapons here. However, the rules also talk about Skirmish Troops, saying "These are named depending on the troop type and include slings, bows and javelins. This is their primary weapon". Now, I don't want to have any of my auxilia as "Skirmishing Troops", because that fundamentally goes against how the auxiliary cohorts operated. I just want an opportunity to give some of them the ability to use slings rather than javelins as ranged weapons, taking advantage of their Flexible Drill characteristic.

Of course, the next question is how can these guys be accommodated within the rules? Well one suggestion (made by David Hunter) is to define them as;

Auxilia with slings          Warriors                8 men. 

Medium Armour             Mixed Weapons    Slings

Aggressive Attack 2       Step Out 1             Drilled, Supra Numerum, Flexible Drill

and field them with the following proviso; 

They may only use slings when skirmishing and only half the men fire, because  loading their slings is hampered by the shields they carry.

That seems reasonable to me, but the alternative might just be to mix them in with a group of auxiliaries with javelins and ignore the fact that they have slings. Personally, I prefer the first idea, but I suppose that it is up to my opponents if they are happy to play against auxiliary slingers.