Or just pre-install some SC-SC APC simplex fibre and use a coupler to join it to the Openreach terminated fibre.
I believe that's technically not permitted: the demarcation point of the service is the RJ45 port on the NTE, anything before that is part of Openreach's service provision.
Of course, if you get a friendly engineer and feed them biscuits, they'll probably install it however you like. But if the service later fails, and an engineer visit is required, and they claim (rightly or wrongly) that the problem is due to an issue with your cable, in theory you could end up paying for the repair.
You would be much better off getting the OR engineer to run *their* fibre all the way. As has been mentioned before, the inner white fibre is very thin. It could easily be tacked to a skirting board, and is no more obtrusive than a traditional telephone cable.