Maybe if they added more earnings alternatives besides the traditional faucet, like micro jobs offers, it would be already an extra incentive for new users to stay more time on the platform, what would also boost the referral program. What happens right now is that common users who are trying to make some extra income online see no point in claiming 4-5 satoshis every hour and dice or slots aren't enough to keep them active, as they lack money to deposit and play. Promotional codes shared at this forum thread or social medias to give users extra rewards would be also an interesting bonus to attract more members to freebitco.in.
While adding microjobs might be a good idea, I don't think it really fits in their 'business'. Nowadays it is just very difficult to find new referrals on freebitco.in as it is the oldest faucet around and the most popular one. Finding referrals, keeping them active is always the challenging part (on every site). On freebitco.in you also have the opportunity to share some of your commissions with your referrals, so that can be one way to keep your referrals active.