Anyway, I recently discovered an alley street in Sugamo that fits the bill quite well. There are at least 3 blowjob bars (well, not quite bars as they don't serve alcohol as far as I can tell) within 1/2 a block; perhaps there are even more BJ places further down the street, I haven't checked yet.
I tried Jan Jan three times and it was pretty good, especially when one considers the cost was only 3,000 yen (about $35--hey it's Tokyo, that's a bargain!). The protocol is there is a reasonably friendly tout outside the place who directs you in (and down the stairs). You then pay the fee and are led to a booth (nothing is real private in these places) where you sit down and they bring you some tea. Within maybe five minutes a girl appears, introduces herself, and gets down to business.
Business consists of pussy fingering, breast sucking, DFK if you trust the mouthwash they use (ewwwww!), and a BBBJ. Music is playing in the background, and you are usually done fairly quickly.
I suspect you can ask for a particular girl (in some Japanese establishments this costs more, but I doubt it at this place) but if you, like me, don't know Japanese it would be difficult. I would say the girls are not stunners (no surprise) but on average acceptable for the task at hand.
What follows are directions with pictures to Jan Jan (although you won't see the name of the place in English on any signs). Note that Jan Jan seems to be the second blow-job bar on the right-hand side of the alley, recognizable by the touts standing outside (next to pictures of some of the girls). The first place on the right usually charges 4,000 yen, although that may be dependent on the time of day because I once saw them charging 3,000. There is also a similar place to the left (maybe just before the first one on the right, or perhaps directly across from it) which seems to charge a ridiculously low 3,000 yen for 2 girls giving you (presumably consecutive) blowjobs. I am fairly certain the latter place only gives covered blow jobs, and am unsure about the 4,000 yen place.
Okay, to get there you probably want to take either the Yamanote line or Mita line to Sugamo, which on a map is not so far from Ikebukuro. If you use the Yamanote line, as you go out the exit gate, hang a right until you see the South Exit and Front Exit, essentially next to each other. Because the South Exit is currently undergoing construction, I'll give directions from the Front Exit, although the directions would almost be he same from either.
Parenthetically, if you arrive by the Mita line, you have a bit of a walk to the exit gate; from there look for the same South and Front Exit signs.
As you go out the front exit turn left and walk on the bridge that goes over the train tracks.
In the picture you can see off to the left a building with a red sign above a yellow sign. You are going to head in that direction because the alley/street is immediately to the right of that sign and building.
Here is a closer view of the area you need to go to. You can see the red sign (with the name Diabro) above the Yellow sign (with the words 4F and MAP); again the alley is just to the right of this.
And here is the alley you will want to walk straight into:
Finally, the red sign with the "B1" at the bottom is where Jan Jan is. As you walk the 1/2 block in, and get to this sign, you will have already passed the other two BJ places.
Good luck!