You only add UKash voucher to WME (euros) Purse, you have create a WME purse if you haven't already created one.
Then you can Transer from WME (Euros) purse to WMZ purse (USD) - don't know the currency rate but you'll probably loose some money due to currency rate.
Check UKash Currency Rate Here:
https://direct.ukash.com/forexViewer/ExchangeRates.aspxI wouldn't recommend using FasterPay to add money to your webmoney account, they charge 2 USD to add money and maximum you can add at a time is 13 USD.
If you use Liqpay you need to link a card to liqpay account first, they will take a small amount of money from your account and then you use that amount as a code to link your card to your liqpay account, so if the amount is 1.24 USD then the linking code is 124. you use the chat support , they can help with linking your card.
Fees for UK:
LiqPAY Account, Visa Card of CIS, 1.95 USD + 1%, from 3 up to 6 business days, up to 250 USD max per transaction
up to 500 USD max per day
https://liqpay.com/?do=pages&p=feesPaypay, 1 USD= 1.30 USD
use Currency converter
https://www.paypal.com/uk/cgi-bin/webscr?cmd=_convert-currency-genericIn my opinion Paypal is cheapest, theres no extra fees and its fast.