So what I'm wondering is, am I allowed to say "due to the way my mind currently works I'm choosing to optimize X by not actively committing to doing X" without running into the "you're not trying hard enough" kind of argument?

I'd say yes, even if it would only be to prevent worse things.

To quote one of Yvain's recent posts:

The rationalist community tends to get a lot of high-scrupulosity people, people who tend to beat themselves up for not doing more than they are. It’s why I push giving 10% to charity, not as some kind of amazing stretch goal that we need to guilt people into doing, but as a crutch, a sort of “don’t worry, you’re still okay if you only give ten percent”. It’s why there’s so much emphasis on “heroic responsibility” and how you, yes you, have to solve all the world’s problems personally.

This might be a similar situation. If you choice is doing nothing vs doing something, doing something is pretty much always better. (Assuming you do useful things, but let's take that for granted for now.)

If you follow the standard Less Wrong interpretation of utilitarianism, you're pretty much never doing enough to improve the world. Of course no-one actually holds you to such unreasonable standards, because doing so would be pretty insane. If you tried to be a perfect utility maximizer, you'd end up paralyzed with decision fear, anxiety and/or depression and that doesn't get us anywhere at all.

Since I'm quoting people, here's a useful quote to have come out the tumblr rationalists:

[Considering yourself a bad person because utilitarianism] is like saying Usain Bolt is slow because he runs at such a tiny fraction of the speed of light.

To make that more specific to your own situation:

Maybe saying "Alright, I'll give 10% of my income and we call it that," doesn't work for you, for whatever reason. Of course you're allowed to figure out something else that does work for you. That's what rationality is all about. Reaching your goals, even if the standard approach doesn't work for me.

That being said, it might still be interesting to see if changing the way your mind works isn't easier. (It probably isn't, but just in case...) From what you describe, it sounds like a form of akrasia which you might be able to work around in other ways than a variant of planned procrastination