O Rxvt Unicode tem suporte para isso.
de man urxvt :
-lsp number
Compile frills: Lines (pixel height) to insert between each row of the display. Useful to work around font rendering problems; resource lineSpace.
-letsp number
Compile frills: Amount to adjust the computed character width by to control overall letter spacing. Negative values will tighten up the letter spacing, positive values will space letters out more. Useful to work around odd font metrics; resource letterSpace.