The new recruits included a former vice president, home minister and lawmakers.
JP leader Gasim Ibrahim announced he was open to talks with other parties to challenge the MDP.
PPM MP Abdul Raheem Abdulla has also thrown his name into the hat.
Maldives tourism is politicised partly because of how it emerged.
Mohamed Nasheed and Gasim Ibrahim both live in exile.
Siyad Gasim is the son of a wealthy and influential opposition leader.
There was a secret ballot during a Jumhooree Party meeting.
Jumhooree Party MP Ali Hussain dismissed speculation that the exiled business tycoon has made a deal with the government.
Mohamed Nasheed and Gasim Ibrahim have both sought asylum overseas. Both have said they want to run for office.
Gasim Ibrahim was found guilty of attempted bribery last August.
Exiled former president Nasheed and JP leader Gasim Ibrahim are under investigation for refusing to return to prison after their medical leave expired.
The Adhaalath Party and former president Gayoom's aides denied any agreement to back a JP-led coalition in September's presidential election.
The opposition appears divided in its quest to field a unity candidate.
The conglomerate, owned and run by self-exiled Jumhooree Party leader Gasim Ibrahim, is said to have for paid for luxury Malaysian properties for two top judges.
The veteran lawmaker has been described as the ideal candidate because of his efforts to unify the parties and political leaders within the Maldives United Opposition.
Villa Group's bank accounts were unfrozen on Wednesday, having been frozen, unfrozen then frozen again in recent years.
Villa Group has experienced several setbacks since the Jumhooree Party split with the ruling coalition and allied itself with the opposition.
