To achieve this, I'd try reaching out to a couple of similar companies that have similar user bases, where you could do a similar deal.
Write a sales-y email describing the growth of the product, IE, 15% day on day growth, 600 users, good engagement, etc. Then drop that you've been approached by a similar company, and you're looking for a company to partner with, on both this application, and future applications.
And, boom. Once they're interested in bidding, you're suddenly negotiating from a place of power.
Don't forget that you have built something thats very valuable - an application that's growing, that has active users. Ensure you get a fair price for what you've done. And the best way to get a fair price, is by getting a better feel for the 'market value' of your partnership by talking to some other companies.
I wouldn't be too concerned about the idea that "breaking even is harder". If you can find a great partner with a X.X million person built-in user base, you'll be able to replicate this success many times over, for a mutually beneficial partnership. And with a couple of offers on the table, you'll be able to negotiate more favourable terms as well.
You'd definitely be able to negotiate a better split than 50/50. Plus, during the negotiation process, you'll be able to put some interesting benefits on the table to help you get an even better deal, such as - the partner company you chose will get first right of refusal on the next 2 products you generate.
Anyway, best of luck!