I think the first thing you would need to do is start a blog. It's the whole 'eat your own dogfood' thing. If you had a blog you could do linking agreements with other bloggers to spread the word, and you would be able to better test your service.
Lets face it, todays "blogs" are nothing but little PR agencies, and your advice really reads as "start your own PR firm".
Get real, running a successful "blog" is equally hard to running a successful business, and he already trying to run one. Starting a real blog is easy: you just write what's on your mind, but those blogs have nothing to do with business and usually have an audience of 10-12 friends and family members.
Wufoo gets a significant portion of their traffic from their (excellent) blog. 37signals got pretty much all of their initial uptake from people who read their blog. Not because they talk about how awesome their product is...but because they help people learn new things, solve problems, and enjoy their time on the web a little more.
If you want to call a blog a "PR firm", that's fine. Most of us are doing our own PR, as well, and if blogging fits into that line item on your budget, that's fine. The OP wants to take advantage of blogs without blogging, and people are telling him that it doesn't work that way. Nothing you've said counters that advice.
The question was specifically about getting the word out to bloggers I don't see any better way to do that than to BE a blogger and reach out to the audience. It also just so happens that being a blogger will make it easier to test out his app and see what is and isn't good.
If you don't have a blog, or know any bloggers, how do you know this app solves a need?
Dogfood it!