Adding yeast to secondary

Okay, I am making a strong (imperial-ish) red ale. My original gravity was 1.081. I intended to bring it to a final point at most of 1.020, or if I can even lower.

I was using 2 packs of WLP004 (Irish Ale Yeast). According to reviews it is possible to reach 8-8.5% of ABV with it. After 5 days fermenting process stopped and for last 5 days there was no activity. The gravity stopped at 1.030 and the ale a little bit too sweet.

The temperature of the carboy was within 64F-68F depending on time of the day. I am considering adding more yeast and keeping a temperature at 68F-69F (by using a heating belt at night).

Should I add WLP004 or can I use different one and combine them with WLP001 or WLP07? How much should I add? What are my other choices?

I'm kinda of trying to finish the bath in 2 weeks and condition in bottles for another 3 weeks and serve it by the first weekend in April...

Thank you for your help.

Thank you, everybody. I found an answer. Apparently, the rest of the sugars in my beer are not fermentable. I tried to run the recipe through the recipe calculator, and it says that with WLP004 the final gravity would be 1.029. If I used WLP007 it would get to 1.026.

With IBU of 86 and 1 week of dry hopping with 1oz of Simcoe, it is not bad. Not quite what I was hopping to get, but still good (I'll just call it a know-how).

I will be more accurate next time.

PS. I don't have enough space for full grain, thus I'm doing extract beer. With less control over my wort, it is little bit tricky.