Modafinil can definitely be taken sublingually, however be aware you are going off label with how you are using it and so are increasing chances of adverse reactions / side effects.
There are at least two patents I know of from searching scholar.google.com that reference sublingual modafinil specifically for the purposes you describe (shortening the sometimes overlong effects). According to the research I've read sublingual modafinil is definitely effective for more rapid onset as well as shorter duration due to the fact that mucosal and sublingual absorption bypasses the gastrointestinal tract.
One issue a lot of people have with sublingual ingestion is the taste. That said, modafinil is not that bad, especially compared to some of the nastier nootropics I've ingested orally (pramiracetam and sulbutiamine come to mind, instantly).
A single uncoated 100mg tablet of modafinil will contain about 113mg of pharmaceutical grade excipients like lactose monohydrate, crospovidone, cellulose, microcrystalline, starch, silica colloidal anhydrous and magnesium stearate. This may make it a bit harder as it's a lot easier to absorb small amounts sublingually. ). I had some fl-modafinil recently that was in powdered form so it was perfect for the task. If you can luck out and find some good pharma grade moda that is in powdered form this would be your best bet.
Oh, that reminds me, do NOT attempt sublingual or other routes of administration that bypass the gastrointestinal system with analogues like adrafinil since adrafinil is actually a pro-drug that metabolises into modafinil after liver bypass it will render it inactive if it doesn't go through the gut metabolism.
Another way to induce a more rapid onset (and shorter duration of effects) is to take the tablet on an empty stomach. Bonus points for crushing it first so it doesn't have to be fully broken down in your stomach acids before it takes effect.