By coincidence I flew exactly this profile this morning. Leaving the BIG hold I was at 254t so, as you have deduced, 180kts can only be flown at F10. We don't cheat at LHR anymore as ATC can see our mode selections
Thus I called F1 approaching BIG for the "leave heading 265/ speed 220" and then F5 outbound to enable an actual 220kts to be selected and flown. Mrs director called for the usual turn-in over Crystal Palace "left heading 360/speed 180" which I anticipated by calling for F10 about 5 sec before her (psychic or what?). Therefore I was easily able to fly the speeds required and by selecting V/S of about 700 fpm a continuous descent profile as well.
All that was needed was a similar anticipation for F20 to be able to fly 160 to 4DME on the glideslope and throw the Dunlops out at 1500' for a stable approach gate at 1000'.
By getting all the flap selections called for in a timely fashion the slow extension time can be allowed for - all it takes is a little forethough.