referencing methods dynamically results in Type 'Numeral' has no call signatures

[Mottoweb]

I am trying to access methods of numeral dynamically in typescript like so:

numeral(currentPrice)[method as keyof Numeral](priceDiff).format('0.00000')

which results in Type 'Numeral' has no call signatures type error, as far as i understand its because type Numeral is declared as class rather than interface, any help for a workaround or a fix would be much appreciated