Here is the only way to do this that I know without you being penalized, and it will take a reseller to get it done for you.
You get the 5 minimum, then have the 2 licenses merged into a single 8 user, and the total time of both licenses is averaged across 8 users. This way, you lose no time, and you get a single license with single anniversary.
Sincerely,
J.R. "AutoSandbox Guy" Guthrie
"At this point in time, the Internet should be regarded as an Enemy Weapons System!"