Magus of the Future might be fun. UUU for a lot of potential card advantage, especially when combined with Top. Not sure it is worth it, just throwing it out there.
Also you could run Trinket Mage which is ideally costed for Heartless Summoning and gets Lotus to make Future easier to play.
In my set review, I mentioned Trinket Mage and Auriok Salvagers, as a combo I'd consider including with Heartless Summoning.
I've been trying to stay out of this, but I'll mention Imperial Recruiter again since it grabs all three of the mentioned cards.
Like.
