I've looked around for a while looking for ways to hack-increase the maxplayers for TF2 servers, I found a method of adding 2 slots to the maximum 32 slot valve rule.
Step 1: Download and install Oil plugin.
This adds a slot to any server with a simple cvar.
Step 2: When oil is working, you should be getting a 33 slot server. Nothing special, everybody has those now a days.. time to take it to the next level, put tv_enable 1 in your server.cfg file. This enables SourceTV and adds an extra slot so the SourceTV bot doesn't waste a precious slots.
Step 3: Now kick the SourceTV bot every time a maps loads. You could add some auto executing file that does this for you. Enjoy your new 34 slot TF2 server!