Adding multiple sip headers in call file

I am needing to add 3 custom headers to an outgoing call placed using a call file. I am using the commands:

Set: __SIPADDHEADER=x-var1:value1
Set: __SIPADDHEADER=x-var2:value2
Set: __SIPADDHEADER=x-var3:value3

the first line is in the invite but the second two are not. Is there a way to make this work?