Plotting irregular raster object with tmap

I would like to use tmap R package to plot a RasterStack object. The problem is that the coordinates are not real coordinates, but rather climate variables, so I can not specify a valid reference coordinate system. I can plot this object in ggplot and lattice, but I would really like to do it in tmap.

> temp_object
class      : RasterStack 
dimensions : 400, 550, 220000, 1  (nrow, ncol, ncell, nlayers)
resolution : 0.1, 10  (x, y)
extent     : -20, 35, 0, 4000  (xmin, xmax, ymin, ymax)
crs        : NA 
names      :          X1 
min values : 0.001695915 
max values :   0.1038332 

> tm_shape(temp_object, bbox=tmaptools::bb(matrix(c(-20,0,35,4000),2,2))) + tm_raster()
Error: The projection of the shape object temp_shp is not known, while it seems to be projected.

If I try to specify a projection, I do get my plot, but the aspect of x and y is not OK and I did not find any argument in tmap R package, which could give me a desired aspect ratio.

crs(temp_object) <-  "+proj=lcc +lat_1=48 +lat_2=33 +lon_0=-100 +ellps=WGS84"
tm_shape(temp_object, bbox=tmaptools::bb(matrix(c(-20,0,35,4000),2,2))) + 
  tm_raster(legend.show = FALSE) + tm_grid()

Is there any argument in tmap, which would enable me to plot this raster with random aspect ratio? An example of such argument in ggR R package is argument coord_equal = FALSE.

  library(RStoolbox)
  ggR(temp_object,  coord_equal = F, geom_raster = 1)