Solved

Player Promotion

Hello,
As of 18th April 2020, the support team will no longer be accepting promotion requests (https://igpmanager.com/forum-thread/34407)

However, there are 2 things your leaguemate could do:

1. Leave and rejoin - Your leaguemate could leave your league, join a different league and  get promoted into the Elite tier, and then re-join your league. 

2. Wait - Your leaguemate could wait until the Pro tier gets populated enough to activate promotion, and then get promoted manually to your Elite tier. 

Hello,
Sorry for any confusion, but when I was writing my original reponse, I missed a few words out (now edited in in red). 

Your league mate needs to join another league and get promoted by finishing in the top 2/4, leaving the league won't be enough to promote him. 

Hello,
To get promoted, your leaguemate will have to leave your league, join another league and finish within the top 2/4. This will promote him to Elite and then he can rejoin your league in Elite if he wants. 

Hello,
If you would like to suggest this, please create a new thread in the suggestions subforum, however, in my opinion, allowing hosts to promote other managers could be up for exploitation - the host may promote a team in order to restrict them winning the championship. 
However, you can still suggest this on the Suggestions subforum to see what other managers think and whether the developers would be willing to add this.