How can I multiply a float and a generic type?

I'm programming in Unity 3.4.2 on OS X using C#.

I have a class like the following:

class Foo<T>
{
    public T DoFoo(T bar)
    {
        float aFloatValue = 1.0f;
        // Do other stuff...
        return aFloatValue * bar;
    }
}

When Unity compiles this class, it gives me this error message:

error CS0019: Operator *' cannot be applied to operands of type float' and `T'

I know that the types I provide for T will support multiplication with float. How can I implement generic multiplication in this case?