Custom Prestige Class question

[Fiordhraoi]

Hey all,

Trying to make a prestige class, and I would like to add a feature that is similar to the +1 caster level in a previous class sort of thing. In this case though, I would like to continue power progression of previously held domains in addition.

Example: I have a Cleric 6 / Prestige Class 6. Cleric has the Air domain. Normally, if this Cleric takes a prestige class, that means he'd have the level 6 air domain ability (Electricity resistance 10). However, I would like Hero Lab to add the prestige class levels to the Cleric for the purposes of domain powers, meaning he'd have access to the 12th level Air power (Electricity resistance 20).

Suggestions?