Basemap does not respects False Easting or False Northing

While creating a basemap from an EPSG code with the x_0 or y_0 (False Easting and False Northing), the Basemap instance does not respect those values. I tried with 'tmerc' projections only because it's of my interest. I leave an example:

Suppose I want to use this EPSG basemap:

# POSGAR 94 / Argentina 1
<22181> +proj=tmerc +lat_0=-90 +lon_0=-72 +k=1 +x_0=1500000 +y_0=0 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs  <>

It can be found in "basemap/data/epsg" file.

Then I create the basemap and print its parameters:

from mpl_toolkits.basemap import Basemap

lon_min, lat_min = -75, -45
lon_max, lat_max = -70, -40
bm = Basemap(epsg=22181,
             llcrnrlon=lon_min, llcrnrlat=lat_min,
             urcrnrlon=lon_max, urcrnrlat=lat_max)

print bm.proj4string

I get the following output:
+a=6378137.0 +b=6356752.31425 +k_0=1.0 +y_0=-5012640.49452 +lon_0=-72.0 +proj=tmerc +x_0=236540.642361 +units=m +lat_0=-90.0

As we can see, the Basemap overrides the false easting and false northing information:
+x_0=236540.642361 +y_0=-5012640.49452

It would be great that the Basemap respect those values and even better if they can be passed as arguments while initializing it in the usual way (without using EPSG codes), for example:

bm = Basemap(projection='tmerc',
             lon_0=lon_0, lat_0=lat_0,
             x_0=x_0, y_0=y_0
             llcrnrlon=lon_min, llcrnrlat=lat_min,
             urcrnrlon=lon_max, urcrnrlat=lat_max)

从 Basemap 构造函数和使用 basemap/data/epsg 中 22181 条目的 EPSG 查找开始；重现 tmerc 示例，并检查投影参数如何变为 proj4string。确认 EPSG 提供的 x_0 和 y_0 会被保留，并确定应如何处理等效的构造函数参数。完成的标准是示例保留两个假偏移量，并且回归覆盖验证它们。