@layman,
Sure, but I'm not sure if we're speaking in a hypothetical manner or just a conditional in respect to the sentences I began with.
I can do that for you, if you (would) prefer.
In this sentence, I have questions about the "would" because it's odd to me to use it after "can". The can should be "could", shouldn't it?
I could do that for you, if you would prefer.
OR
If you would prefer, I could do that for you.
Whereas "will" makes more sense to me in relation to the preceding can.
I can do that for you, if you will prefer.
OR
If you will prefer, I can do that for you.
It does sound odd, which leaves me thinking: "if you prefer, I can do that for you" is the best sounding option, unless the function of "would" here is not actually as a marker of a conditional statement but rather to soften/make more polite the statement as has been said on other places I have checked on the interwebs. If that is true, however, that wouldn't make it grammatical, just formal.