You have quite a few alternatives and most all can be pounded into a powder and suspended in water or tuna juice and administered by syringe if need be. Medical therapy includes either over the counter or prescription stool softeners and/or laxatives. Over the counter products include:
docusate sodium/dioctyl sulfosuccinate (Colace, e.g.) dosed at 50 mg/cat every 12-24 hours
mineral oil flavored with vegetable oil at 10-25 mL/cat per day
hairball remedies containing petrolatum
Prescription products include:
lactulose dosed at 0.1-1.25 mg/lb every 8-12 hours - lactulose is the most effective stool softener and is given to effect daily to maintain a soft to semiformed stool (usual dose after titration is 1-4 mL/cat every 8-12 hours
cisapride 0.05-0.5 mg/lb every 8-12 hours or 2.5-5 mg/cat every 8-12 hours - cisapride is a prokinetic drug - it stimulates colonic motility
Bulk forming laxatives (cellulose, psyllium seed) won't be effective in cats prone to dehydration or in cats with poor colonic muscle function because their mechanism is similar to high fiber diets (see below). The can be helpful for simple constipation, however. Psyllium seed (Metamucil) can be added at 1-4 tsp/canned food meal.
Stimulant laxatives (e.g., bisacodyl, castor oil, cascara) shouldn't be used for relieving constipation but are best used as a preventative in cats that still have normal colonic function.
Prokinetic therapy may assist smooth muscle function in cats with recurrent constipation or obstipation. The most effective drugs are the prescription serotonergic agonists such as cisapride and over the counter histamine H2 receptor antagonists such as ranitidine (Zantac) dosed at 0.5-1 mg/lb every 8-12 hours.
A high fiber or low-residue diet may be of value. High fiber diets induce colonic contraction when my patient still has a functional colon and is well hydrated. I need to avoid high fiber diets in patients that are prone to dehydration (can exacerbate it). Low residue diets are often best in patients with chronic recurrent episodes of obstipation or true megacolon because they reduce the amount of material reaching the colon and make it easier to keep a soft stool. The best of these diets are available through your vet.
Please respond with further questions or concerns if you wish.