You can get single mode fibre (aka the stuff that is used for FTTP) that has a bend radius of 10mm aka 1cm. Here is some simple single mode APC to APC cable with such a bend radius.
The postage is going to be more than the cable costs There is no need to get anyone in to splice any cable a simple APC SC/SC coupler for a few quid is all you need.
I can't see a listing on fs.com for a single one but give 10 of them are under £5 hardly a large financial loss if the remaining 9 go in the bin.
I am assuming that Openreach are using angled physical SC connectors (APC) rather than the normal "flat" ones (UPC). All the photos I have seen show green connectors rather than blue which would be standard for APC however some of the Openreach documentation suggest they use UPC connectors but I think that is a mistake. Normally APC connectors are used in FTTP installations due to the lower optical loss.