Get related data without relationship between tables

When I have two models with one to many relationship, they look like the models below:

public class Student
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int StudentID { get; set; }

    public string Name { get; set; }

    public int ClassID { get; set; }
    [ForeignKey("ClassID")]
    public virtual Class Class { get; set; }
}

public class Class
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
    public int ClassID { get; set; }

    public string Name { get; set; }

    public virtual ICollection<Student> Students { get; set; }
}

This means that I can use the include method to get the related data. Now I work on a project with more than 600 tables. For these tables there are no relationships and I can not create relationships between the tables. Is there a way to link the models somehow so that I will be able to get the related data?