PPCGeeks - Wirefly Upgrade, swapping phones

I have a Sprint Family Plan with 4 lines on it with 2 of the lines that have the $150 off an upgrade and plan extension.

I've been seeing these Wirefly promotions regarding deals with upgrading an eligible family plan line. Here is my question....

Can I upgrade one of my eligible lines of service and pay the promotion price, get the phone, and then activate that phone on one of the ineligible lines???

If anyone has any experience with doing this or if this isn't possible please let me know.

I know with sprint you have to deal with rebates and they want you to have the upgraded phone on the eligible line for 30 days or something like that in order to receive the rebate.

Thanks.