Default Values for a mutli select box on an infopath form

Hi,

So I have created a multi selection box within InfoPath and connected it to external data which is filtered dependent an two options select before hand by the user.

so at the moment the options that show up are dependent of the combination of values from the two drop downs above... however I wish to have two values which show up all the time no matter what the combination of the boxes above are?

I hope that makes sense, if not feel free to ask some questions to help me get what I need across.

thanks,

Oli