Why not add banking system to the game? Building a stellar bank you get dust overdraft protection, which give you opportunity to spend more dust then you currently got. Over time your dust income per turn will eventually cover your minus account state.

Every 5 turns game will calculate interest rate and automatic withdraw certain amount of dust for using overdraft credit, until you reach positive account state.

Upgrading you bank you could get more amount of your credit?

p.s. yes I am a banker and sorry for my bad English J