[FlexJS] How to set beads based on a condition?

[OmPrakash Muppirala]

I want to show a button in my itemrenderer.  Depending on the data value, I
want to enable or disable it.

In the mdl example, I see this:

<mdl:Button text="DISABLED" raised="true">
                <mdl:beads>
                    <mdl:Disabled/>
                </mdl:beads>
</mdl:Button>

Is there a way to conditionally set a bead?

I'm guessing the syntax would be something like this:

<beads>
    <Disabled if="{data.twitter == null}" />
</beads>

I don't want to resort to writing AS3 instead of MXML just for this
usecase.

Thanks,
Om