Problem With First name and Last name in the Contacts module tab

Problem With First name and Last name in the Contacts module tab

4]  First name-Last name problem in Zoho CRM
a]  Last Name is  required field while saving any name of customer inside Contacts.
b]  very often I do not have last name known to us of the customer - so put first name into last name field
c]  do not want to put first name in both fields [ First name as well as Last name fields]
d] do not want to put some placeholder in Last name field
e]  DO want to use first name in emails while sending emails using mass email and  email templates e.g Dear "First name"
f]  do NOT want to use formal Dear "first name + Last name" in emails - that's just bad
g] DO want to SOMETIMES use FULL name [fn+ln] - in which case it should just show 1st name [instead of some mess for last name].

So my problem is If I don't have last name available of my customer, and as Last name is required field so I have to put first name into Last name Field which makes First name empty. But while sending mass email using email templates I need to use Dear " First name" , but as my First name field is empty, my emails went like[ Dear,] without any name.
How to overcome this problem?