Help with Mr. Malty

I could use a little advice here. Today happens to be both bottling day and brew day. I am making a brew with an OG of 1.075 and realized my starter is way too small. The yeast is a wyeast 1056. I am racking to bottles an amber that had an OG of 1.060 made with 1056. The thought of repitching on the old yeast cake makes me uncomfortable so I was thinking this might work. Could I pitch my starter and make up the difference with some of the old yeast cake by using the slurry tab on mr malty? Is the slurry tab only used for washed yeast? I hate to ruin the beer by under pitching by oh alot.

I use the slurry tab as just that. Slurry from the bottom of a previous brew. No wash.