Is there a way not to call SaveChanges so often in the case of a junction table for a many-to-many relationship?

I need to have an extra field in the junction table of a many-to-many relationship, like so:

public class PersonCompany
{
    public int PersonId { get; set; }
    public int CompanyId { get; set; }
    public Person Person { get; set; }
    public Company Company { get; set; }
    public DateTime HireDate { get; set; }
}

with these 2 classes at the ends of the relationship:

public class Company
{
    public int CompanyId { get; set; }
    public string Name { get; set; }
    public virtual ICollection<PersonCompany> PersonCompanies { get; set; }
}

public class Person
{
    public Person()
    {
        PersonCompanies = new List<PersonCompany>();
    }
    public int PersonId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public virtual ICollection<PersonCompany> PersonCompanies { get; set; }
}

Yet when using it, I have to call SaveChanges on the context too many times for the primary and foreign keys to get their values, like in this example:

private static void AddPersonWithCompanies()
    {
        using (var context = new Context())
        {
            var person = new Person
            {
                LastName = "Dent",
                FirstName = "Juan",
                IsActive = false
            };
            context.People.Add(person);

            context.SaveChanges();

            var comp1 = new Company() { Name = "Universal" };
            var comp2 = new Company() { Name = "Lehmann" };

            context.Companies.Add(comp1);
            context.Companies.Add(comp2);

            context.SaveChanges();

            var pc1 = new PersonCompany() { Company = comp1, Person  = person, HireDate = DateTime.Today };
            var pc2 = new PersonCompany() { Company = comp2, Person=person, HireDate = DateTime.Today };

            person.PersonCompanies.Add(pc1);
            person.PersonCompanies.Add(pc2);

            context.SaveChanges();
        }
    }

I would like to have only one SaveChanges() at the end but can't seem to get it... I get the following exception if these intermediate SaveChanges() are removed:

System.Data.Entity.Infrastructure.DbUpdateException
  HResult=0x80131501
  Message=Unable to determine the principal end of the 'Chapter3.CSharp.Company_PersonCompanies' relationship. Multiple added entities may have the same primary key.
  Source=EntityFramework
  StackTrace:
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at Chapter3.CSharp.Program.AddPersonWithCompanies() in C:\Users\Juan Dent\OneDrive\CSharp\Code First-Code Bundle\B03947_03_Code\Chapter3.CSharp\Program.cs:line 47
   at Chapter3.CSharp.Program.Main(String[] args) in C:\Users\Juan Dent\OneDrive\CSharp\Code First-Code Bundle\B03947_03_Code\Chapter3.CSharp\Program.cs:line 14

Any ideas?

Regards, Juan