No, but you can use the Time Machine to run a firmware 1.5 + 3.40 hybrid on a Slim. Anyway most homebrew is written for the 3.X kernel and up these days so the lack of 1.5 support is not so bad.

Because I love having my old nes games on the road.

"most homebrew is written for the 3.X kernel and up these days"

there are emulators specifically for the slim i.e. nesticle, snes9xtyl, ect. they dont need the 1.5 kernel

edit: from the comments on the link

icedman204 says:

I've tested a few 3.xx kernel homebrews and they seem to work so far :)

June 28, 2008, 3:47 pm

The updating method provided in the link only works for previous M33 Custom Firmwares. Official Sony firmwares must be cracked and downgraded before upgrading to your own custom firmware. Unfortunately for you, you'll have to wait until someone figures out how to downgrade from official firmware 4.01 or higher. I don't know what the newest downgrader goes up to, but my advice is that if you want custom firmware, DO NOT upgrade to any newer Sony firmware updates. Eventually someone will release the appropriate downgrader for you. Sony releases new security measures in each update making every new firmware harder to downgrade, so if you keep updating via Sony's server you won't be able to downgrade at all.

which requires another PSP that has custom firmware on it