serout doesnt support modifiers, you will have to use serout2. gives you more control anyway.
then you can just use

Modifier Operation
{I}{S}BIN{1..16} Send binary digits
{I}{S}DEC{1..5} Send decimal digits
{I}{S}HEX{1..4} Send hexadecimal digits
REP c\n Send character c repeated n times
STR ArrayVar{\n} Send string of n characters

vuala.

phil