Is possible to parse a string as function and reference runtime variables?

Question

I'm trying ExpandoObjects to accomplish custom calculations on some customer data.

For example, there exists some class as (short version):

public class Seller
{
    public Guid Id { get; set; }
    public decimal MonthlyAmount { get; set; }
}

In some process, we need to dynamically create some properties, whose formulas are defined as literals in a dictionary. For example:

var formulas = new Dictionary<string, string>
{
    { "Bonus", "Seller.MonthlyAmount > 1000 ? Seller.MonthlyAmount * 3/100 : 0" },
    { "AmountPlusBonus", "Seller.MonthlyAmount + Bonus" }
}

I would need to create a dynamic class, which allows to have to parse the literal as a custom function.

I have tried the following, without success:

var seller = new Seller();

var sellerEx = new ExpandoObject() as IDictionary<string, object>;
sellerEx["Seller"] = seller;

foreach (var formula in formulas)
{
    sellerEx[formula.Key] = DynamicExpressionParser.ParseLambda(
    ParsingConfig.Default, false, typeof(object), formula.Value);
}

During execution, it complains with "Unknown identifier 'Seller'". How it is Seller unknown, if the expando already has this assignment?: sellerEx["Seller"] = seller?

What would be a working approach for this?

Apart from "Seller", I would like to have other objects as source for calculations, like:

sellerEx["Seller"] = seller;
sellerEx["Schedule"] = schedule;
sellerEx["ProductList"] = productList;

I mean, I expect the Parse to define functions on the expando and take other expando properties as part of its context. Is it possible?