Multi-form User-defined Functions

So I've created a function that generates an equation for a payoff diagram, or if the optional variable is provided, a profit diagram:

Function ECallG(LongPos As Boolean, Price As Integer, Strike As Integer, Underlying As Integer, Optional Quantity As Integer) As Long

    'Provide an equation to graph a European Call Option's payoff, or profit if Quantity > 0

    If Quantity > 0 Then

    'Generate a profit graph

        If LongPos = "True" Then

            ECallG = Application.Max(-Price, (Underlying - Strike - Price)) * Quantity

        Else: ECallG = Application.Min(Price, -(Underlying - Strike - Price)) * Quantity

        End If

    Else

    'Generate a payoff diagram (do not consider the cost of acquiring the option)

        If LongPos = "True" Then

            ECallG = Application.Max(0, (Underlying - Strike))

        Else: ECallG = Application.Min(0, -(Underlying - Strike))

        End If

    End If

End Function

I want to remove the main IF statement, and have a setup that returns a two-form function that is visual similar to the INDEX function.