Doesn't it suck when every other person on your team ditches and you just wanna kick some ass? Well you can! and this is how.
Use other characters to farm you gold. It doesn't matter if they die and in some cases its useful to kill them here and their so their level stays low so they don't yield much more exp then killing creeps. Make sure you don't let the same character kill them over and over also because it makes no sense to make one guy particularly strong. It helps to be on an agility or strength character but its possible with any character. Get yourself a manta, a butterfly, a satanic, and a heart. Then build dagon for extra dps.
When you have all of these items you will likely have gotten a few kills solo here and their. The main thing is that you cannot die. You are the only hero that has to stay alive. It doesn't really matter if they push other lanes just stick to the mid lane and hammer out your farm. Make sure you joke with them a little bit and tell them to commend you for staying. This makes them think you are on their side.
Now surprise them suddenly when they come for you in mid and use every stun and ult you can on your team. Kill and chase back as many of them as possible. They won't suspect an actual attack on them because they have been getting fed most of the game off of your heros. You will quickly go through their tier 1 2 and 3 towers. If it looks like their is time take out a mid raks. If not head straight for rosh. They now know that you mean business when they see you have aegis. Instead of fighting them this time try and avoid them. Get as many characters as you can outside their base. When you see the X's on the mini map finish the mid raks off and go for their ancient towers. You will likely get one before they get back. This is where you make your stand. Its do or die kill them as soon as they teleport in or get them running back for safety. Once your aegis is down get out of there and wait for your bot heros to respawn. Now stop them at your base and go for the finish push.
Congrats you have won solo against five. Either that or your happy you put up such a good fight. Enjoy and give them hell.