Change native Android SIP dialing settings

My SIP Trunk (hooio) has a specific dialing plan: [Country Code][Phone Number incl. Area Code] However, all mobile carriers have a different dialing plan: [Local Phone Number] OR +[Country Code][Phone Number incl Area Code] *The main difference here is the 'plus' character.* All my phonebook entries are geared to work with the +[country][number] plan. But when I dial these using the native SIP client, I get errors - since the trunk does not like the plus (should this not be a standard?). I'd really like to keep using this trunk, and they apparently can't or won't change their dialing plan. The only alternative is to have duplicate phonebooks for mobile vs internet calls - and I don't like my provider enough to waste time on this :( Is there any way to configure rules for dialing with the native client, like removing the plus before dialing?