Mailchimp unique subscriber number MC4WP

I am using mailchimp for a very small club before they go down the path of paying for a membership plugin.

I would like to generate a unique number so each subscriber (member) has a membership number. Not a unique URL.

I have read mailchimp documentation and I am stuck. Can this be done? A php database automatically does this – correct? Can I make the number visible to the mailchimp database and in the welcome email the member receives? It will be hidden on the form.

TIA

<p>
	<label>Email address: 
		<input type="email" name="EMAIL" placeholder="Your email address" required />
</label>
</p>
<p>
    <label>First Name</label>
    <input type="text" name="FNAME" required="">
</p>
<p>
    <label>Last Name</label>
    <input type="text" name="LNAME" required="">
</p>
<p>
    <label>Address</label>
    <input type="text" name="ADDRESS[addr1]" required="">
</p>
<p>
    <label>Suburb</label>
    <input type="text" name="ADDRESS[city]">
</p>
<p>
    <label>State</label>
    <input type="text" name="ADDRESS[state]" placeholder="QLD"
    value="QLD">
</p>
<p>
    <label>Postcode</label>
    <input type="text" name="ADDRESS[zip]">
</p>

<p>
    <label>Mobile Number</label>
    <input type="tel" name="PHONE" required="">
</p>
<p>
    <label>Birthday</label>
PLAY FOR FREE DURING YOUR BIRTHDAY WEEK!
<br>Give day & month only. Your age is a secret
</p>
    <input type="text"
    name="MMERGE5" placeholder="DD/MM">
</p>

<p>
	<input type="submit" value="Sign up" />
</p>