How do you set yourself alight for an infinite amount of time? I've tried all the conditions and the closest I've come is condition 22, which only makes your character complain about fire for a split second, but it doesn't set you alight.
As far as I know, there are no vanilla cheat commands to do what you say...
However, there are 2 things you can do to achieve what you say.
1. Enable buddha mode so you don't die by fire.
2. From a dedicated SourceMod server (or offline listen server), create a trigger multiple dynamically using this plugin and add the output (OnTrigger !activator igniteplayer).
This usage is shown in achievement_idle_inferno, and as I have tested is able to set you on fire infinitely while inside and can activate the B.A.S.E jumper forever unless you die.
Cheers, and hope you can work it out with this strategy.