As far as I know, you just can't buy avios if you IBPlus account is inactive. Otherwise it would be very use to activate them, given the fact that if you want to activate it is to transfer avios to/from it.
In case it is possible for you, another way to grab some fast Avios is to send you IbPlus card to someone in Spain. who could show it at any Repsol petrol station. The avios will show by the end of the month