Someone could, yes, but this is one of those "Give a man a fish..." situations.
Lets say I was to compile for you, the current release with this patch applied. What is going to happen in ~3 months time when 3.13 is released, are you going to be using an out-of-date build forever more...? Are you going to come back and see if you can convince someone else to compile a new build for you...?
Do you see my point?
The development guide linked by saratoga provides all the information you require to patch and compile the Rockbox source code and in many cases the documented procedures assume that the reader has absolutely zero prior knowledge or experience in doing so. It may seem overwhelming at first, and it is easy to assume "It's too hard, I can't do it", but I assure you that you could if you wanted to.
Assuming you have an internet connection with a reasonable speed, a reasonably modern machine, and can read and follow simple direction you will be able to download and patch the source and compile a build in a few hours time. With the added bonus of learning something along the way and not having to be reliant on others.
EDIT: It is also worth noting that this is not "LOD" (Line-Out Dock), but enables switching the 3.5mm headphone jack for use as Line-Out which you can do yourself trivially by simply setting the volume to 0dB.
If you are actually interested in LOD, you can purchase a premade LOD cable for $20 or less from any one of a number of places (simply search for "Sansa Fuze LOD") or make one yourself for even less if you can solder. All you'll need is some 3-core cable, a ridax connector (standard iPod/Sansa dock connector), and whatever it is you want to terminate the cable with (2RCA, 3.5mm stereo, 7mm stereo, etc.). The pin-out from your devices dock is well known and freely available on the internet (simply search for "Sansa Fuze pinout").
The simplest, and cheapest (can't get cheaper than free) method for you is to simply set the volume to 0dB (you can even create an alternate config file to do this and set a shortcut to it). Just remember to lower the volume again before using your in-ear monitors lest you deafen yourself accidentally.