First of all I would cover part of the aspen with newspaper or paper towel so no shavings get stuck. Though if the mouse is dry, it shouldnt be much of a problem.

I would try dangling the mouse, or making it "jump" or "twitch" around on the bottom of the cage. Sometimes they have an instant feeding response. Sometimes it takes them about 10 minutes of watching you struggle to finally grab it (I had to perform the dead mouse dance for about 20 minutes for my little guy yesterday before he finally took it). Sometimes you need to leave the mouse in the cage overnight and it'll be gone the next morning.

It can be frustrating at times, and each snake is different. Once it gets onto f/t consistently though... it's a good feeling. My three year old girl loves f/t rats like a fat kid loves cake. Doesn't think or sniff twice.