Adding an outlet to a 3 way switch on 'far' end
The solution is to replace the traditional 3-way switches with smart switches. Traditional switches need 2 travelers. There are smart switches that need only one wire for switched hot and somehow signal on that wire, freeing up a wire to use as constant hot. However you will need neutral.

If your configuration is:


Panel -> switch -> switch -> light


then you turn a traveler into hot. 

If it is:


Panel -> light -> switch -> switch


then you turn a traveler into neutral. Except you have to be careful with colors so that neutral ends up with the white wire.