I don't know that there is an easy way via the web. However, if you're prepared to do a little programming that simulates a web query then yes, there is a way.

Most programming languages have a library (often called mechanize) which can automate web queries and parse the results. Here is how you could use the Ruby mechanize library:

#!/usr/bin/ruby

require "rubygems"
require "mechanize"

# fetch gene list for K01491
agent = Mechanize.new
page  = agent.get("http://www.genome.jp/dbget-bin/get_linkdb?-t+genes+ko:K01491")
links = []

# get links to each gene page
page.links.each do |link|
  if link.uri.to_s =~ /dbget-bin/
    links << link
  end
end

# fetch and print out FASTA
links.each do |link|
  url   = "http://www.genome.jp/dbget-bin/www_bget?-f+-n+n+#{link.text}"
  fasta = agent.get(url)
  puts (fasta/"//pre").inner_text
end

There are 3 parts to this. The first fetches a page containing the gene results for the query K01491. The second looks for the links to each gene page and stores them in an array. Finally, the last section fetches the FASTA page for each gene, extracts the sequence from between the <pre> tags and prints it out.

In a "real" script you would want more careful checks at each stage, but that's the basic idea.

Alternative way to retrieve sequences included in a KEGG Orthology by using BioRuby.

#!/usr/bin/env ruby

require "bio"

orgs = %w[ tcr tbr ] # kegg organism codes of your interest

# create kegg api object
serv = Bio::KEGG::API.new

# create kegg orthology (ko) object
ko = Bio::KEGG::ORTHOLOGY.new(serv.bget("ko:K04283"))

# get kegg genes entry ids of the given kegg orthology
ko.genes.each do |ary|
  orgcode = ary[0]

  # select kegg genes entry ids of given organisms
  if orgs.include?(orgcode)
    ary[1].each do |entry_id|
      # retrieve sequences in fasta format
      puts serv.bget("-f -n 1 #{orgcode}:#{entry_id}")
    end
  end
end