How can I make my far away command blocks work

Put them in the Spawn Chunks

The Spawn Chunks are a 16×16 set of chunks centered around your world spawn. These chunks are loaded at all times, unless no player has been in the overworld in the last 60 seconds^*.

While some mechanisms are not processed when no player is around, such as plant growth or entities, redstone and command blocks are executed normally.

^{* According to the wiki. However, I have not been able to observe the unloading of the chunks on 1.8.7 in a singleplayer test world. IIRC SP is functionally identical to MP.}

The only option would be to tell the player to set the render distance to at least 13 chunks. This will make sure the Command Blocks stay rendered, and allows them to execute commands. Here is a list if you've placed any command blocks further than 208 blocks:

Source