I see what you mean, you want 3 weeks so someone is only able to partially double vote right? 1 week would allow someone to double vote with all stake..

I think it would be best to completely remove steem power and allow users to vote with steem that has been in their wallet for more than 7days.
Say I have 100 steem in my wallet and I just sent myself an extra 50 steem , my upvote would be worth 100 steem until 11th of march ( 1 week from now) , after 11th my vote would be worth 150 steem.

if I vote for something with 100 steem then decide to send those 100 steem to another account to upvote the same content, the other account will have to wait 1 week for the 100 steem to be included in the upvote, so it would be too late to upvote for the same content. This design seem like it would be more secure and not interfere with user experience, also would remove complexity of having 3 currencies.