I think these should do it, I used a pair of them a while ago with some Tiagra brifters which didn't have aero cable routing:
http://www.chainreactioncycles.com/jagwire-rocket-2-cable-adjuster-shimano/rp-prod150987?gs=1&gclid=CjwKEAjwgo6_BRC32q6_5s2R-R8SJAB7hTG-x-mdC0xxY7J7MBMIMwgONH_D_aAS8DVUj1rDViRYhRoC2U3w_wcB&gclsrc=aw.ds
These are jagwire sport adjusters
"Sport Inline Adjusters Two 50mm lengths of 4mm shift housing with end caps included; not recommended for use with brake systems"
Sorry, I understand the difference and potential safety issue.
Strong Google-fu DJ, bullet dodged, so what's the alternative for the OP's issue, there must be something suitable out there, although if it were me I'd just use an inline one near the brake levers...
@dancing james started
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I think these should do it, I used a pair of them a while ago with some Tiagra brifters which didn't have aero cable routing:
http://www.chainreactioncycles.com/jagwire-rocket-2-cable-adjuster-shimano/rp-prod150987?gs=1&gclid=CjwKEAjwgo6_BRC32q6_5s2R-R8SJAB7hTG-x-mdC0xxY7J7MBMIMwgONH_D_aAS8DVUj1rDViRYhRoC2U3w_wcB&gclsrc=aw.ds