The pure contractual solution would be for the contracts manager (CM) to do the same work inside the Working Areas (WAs) if possible. This could include adding to the WAs by, for instance, making a part of the Head Office an area of the WAs which would be used exclusively to Provide the Works.
However, more common sense approach would be something like : both Parties accept that it will take 30'ish hours of additional time and it is actually irrelevant where the work is done. Ignoring the above contractual solution, it is a bit silly that the CM has to travel to the WAs to do 20 hours of it which could (better) be done elsewhere, so just pay it, albeit as a forecast.
You ask : "Is there a mechanism to recover this ?". See above for common sense response. The pure contractual response is that costs not incurred within the Working Areas are in the Fee.
If an assessment is based on a forecast, then the compensation event is added into the activity schedule and the Contractor gets paid for it once the activity has been completed. If the description of the completed activity made no reference to the location where the work was done, the location then becomes irrelevant. I.e. you could price up the quotation on the basis that the CM does the work in the WAs, but is irrelevant for getting paid it.