Ok, I have a world that seems repeatable that has a perfectly flat area (that is really boring), with a volcano on it, in embark distance of a stream.
I will update in a bit with screenshots, and world cookbook data and instructions. (Be sure to follow them. This world gen data makes DF very unhappy, so doing it wrong will not gen the same world.)
Ok, here's the worldgen data.
Created in DF v0.34.09.
[WORLD_GEN]
[TITLE:BuildRegion4]
[SEED:U2WsYwgciWMgYOwwKWAg]
[HISTORY_SEED:00S6aeQ0Cq2eOYCO8S2m]
[NAME_SEED:caewUuGkAgGagkQyCuwC]
[CREATURE_SEED:acYKScQGcCGOICUwuaE6]
[DIM:65:65]
[EMBARK_POINTS:1324]
[END_YEAR:500]
[BEAST_END_YEAR:100:80]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:1:400:202:202]
[RAINFALL:0:100:101:101]
[TEMPERATURE:25:75:101:101]
[DRAINAGE:0:100:101:101]
[VOLCANISM:50:100:101:101]
[SAVAGERY:0:100:101:101]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[MINERAL_SCARCITY:2000]
[MEGABEAST_CAP:50]
[SEMIMEGABEAST_CAP:100]
[TITAN_NUMBER:20]
[TITAN_ATTACK_TRIGGER:50:0:100000]
[DEMON_NUMBER:22]
[NIGHT_TROLL_NUMBER:11]
[BOGEYMAN_NUMBER:11]
[VAMPIRE_NUMBER:11]
[WEREBEAST_NUMBER:11]
[SECRET_NUMBER:22]
[REGIONAL_INTERACTION_NUMBER:22]
[DISTURBANCE_INTERACTION_NUMBER:22]
[EVIL_CLOUD_NUMBER:11]
[EVIL_RAIN_NUMBER:11]
[GOOD_SQ_COUNTS:6:63:127]
[EVIL_SQ_COUNTS:6:63:127]
[PEAK_NUMBER_MIN:3]
[PARTIAL_OCEAN_EDGE_MIN:1]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:50]
[REGION_COUNTS:SWAMP:66:0:0]
[REGION_COUNTS:DESERT:66:0:0]
[REGION_COUNTS:FOREST:264:0:0]
[REGION_COUNTS:MOUNTAINS:528:0:0]
[REGION_COUNTS:OCEAN:528:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:528:0:0]
[REGION_COUNTS:HILLS:528:0:0]
[EROSION_CYCLE_COUNT:250]
[RIVER_MINS:25:25]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:2750]
[CAVERN_LAYER_COUNT:3]
[CAVERN_LAYER_OPENNESS_MIN:0]
[CAVERN_LAYER_OPENNESS_MAX:100]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:100]
[CAVERN_LAYER_WATER_MIN:0]
[CAVERN_LAYER_WATER_MAX:100]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:15]
[LEVELS_ABOVE_LAYER_1:5]
[LEVELS_ABOVE_LAYER_2:1]
[LEVELS_ABOVE_LAYER_3:1]
[LEVELS_ABOVE_LAYER_4:1]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:1]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:25]
[MOUNTAIN_CAVE_MIN:25]
[NON_MOUNTAIN_CAVE_MIN:50]
[ALL_CAVES_VISIBLE:1]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:30]
[TOTAL_CIV_POPULATION:15000]
[SITE_CAP:264]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:528:1056:528]
[RAIN_RANGES:264:528:264]
[DRAINAGE_RANGES:264:528:264]
[SAVAGERY_RANGES:264:528:264]
[VOLCANISM_RANGES:264:528:264]
It will make 2851 rejects, but first will complain about volcanism. Press "t", then about elevation, press "c". It should then generate the world out to 500 years.
There is ONE site that meets your desired criteria. It is actually quite boring. Has everything you need for a booming glass industry.
Here are the screencaps from the embark screen, and a cap of prospector.
As you can see, the entire area is flat as a pancake, except for the volcano itself.
Prospector says this:
Note that there is a nearby stream, which means fishing opportunities, as well as easy obsidian manufacture.
*edit #2
I just did a test embark at the site. It is surrounded by a thick (6 to 7 tiles) rind of red sand. Essentially, a gaint sand dune, filled with magma, standing out in the middle of an equitorial savannah, minding its own business.
The site has ropereeds if your embark encompasses part of the stream, so clothing and bags should be a sinch. Also, sand digs easily. If you wanted to, you could spend a few seasons stripping the sand burden off.
It is very tall. 20z. Be careful releasing the magma. It is likely to start a world destroying fire on the grassland below.